Kate Copestake, 43, was an industrial designer when she met Kevin Bulmer, 37, a graphic artist. In 1985 they moved in together, and founded the computer games company Synthetic Dimensions, which is now valued at £11m. It is about to launch Astro Knights on TV and the internet

Kate Copestake: In the early 1980s I bought a three-bedroom house in Solihull and I took a job selling advertising space for Prestel while I waited for a big design assignment to come in. Kevin was working next door as manager of a design and print company.

Kate Copestake: In the early 1980s I bought a three-bedroom house in Solihull and I took a job selling advertising space for Prestel while I waited for a big design assignment to come in. Kevin was working next door as manager of a design and print company.

Within a month I was working for him, but he was planning to start his own business and asked me to join him. Half-joking, I thought my contribution would be my house as the office if Kevin would give me half the business. He agreed, and moved in, which wasn't quite what I'd meant. I'd gone to my parents, and when I got back he was there. It all happened in three days, our relationship, the company and the house.

Kevin was the sanest, most grounded person I had met, and we were the best of friends. He had taught himself how to program and design computer graphics. What we set up was primarily a design company doing letterheads and logos, but we had this sideline in games for home computers, which were becoming popular.

Because computer games was a fledgling industry there was no way we could get a bank loan. But we had credit cards, so we pushed those to the limit, and lived on credit for six months. It was astonishingly brave or ridiculously stupid, but I had the collateral of the house so it was calculated.

My design training was in glass, metal and ceramics, all of which are to do with texture, shape and the way light reacts with objects. Computer games and modelling was a natural progression for us. Within about six months, Kevin had a great design for the games publisher US Gold, which was bought by Eidos. Arcade games were being converted for the home computer, and we moved from that to our own titles.

Developing computer games was essentially a back-bedroom industry, in our case. You came up with a concept and sample graphics, took them to a publisher and they might agree to pay monthly milestones. In doing so, they put up most of the risk, so we would only get a 15 per cent royalty.

After nine number one hit games, to progress and get a bigger share of the cake, we were going to have to restructure and put forward more of the money ourselves. Also, nobody had heard of us because as developers we weren't getting the publicity. I had been writing scripts, designing graphics and doing character embellishment, but in 1995 I decided to step back and use my talents to promote the company. We looked at different ways to meet investors.

After one such presentation we met Jim Driscoll, maker of The Shoe People and now our corporate development director. He was a director of Sanctuary Music, and they had put a lot of money into developing a game for the band Iron Maiden. Jim asked us to help finish it, but we took a look and said we were sorry, we thought it was quite dreadful.

He was impressed by the fact that we would walk away from the money and said: "Can you write another one from scratch if we co-fund it?" That was the start of a relationship with Iron Maiden which led to the game Ed Hunter, released with an album of the band's hits.

Over the years there have been people eager to buy into our company, but we wanted to go it alone. Kevin has the most amazing mind, he's a true innovator, and these creations were our babies and we wanted the best for them.

With the Ofex listing last year, we sold 15 per cent of the company to raise £1.5m for expansion. We had no problem because we had been in profit every year. I was brought up to look after the pennies. If you're working in an abstract business, you've got be able to walk into a bank and show them you've got good business sense.

Kevin is the visionary, and his work is leaps and bounds ahead of anything around. In the early 1980s he was saying: "Why aren't computer games made into toys or on the front of magazines?" He ranted for years before Tomb Raider came out.

We were sure from the beginning that Astro Knights was fantastic. It was Jim's idea, and in 18 months we've made it a must-have. We have described it as Star Wars meets The Simpsons. We have both grown up enormously since we started, but we still work ridiculous hours.

We do argue and it's easy for people to think: "Oh, they're having a domestic", but if you are a focused person, you can be too blinkered and you need someone to come in from the left-field. We're passionate but we don't fall out.

People ask, how do you live, work and play together? I couldn't imagine any other way. We have a double Jacuzzi at home and every Sunday afternoon we fill the bath, get in, open a bottle of champagne, lie there for three hours and discuss the future of the company.

Kevin Bulmer: I remember my first encounter with a Space Invaders machine in a pub; I watched this complete whizz. I had a go, but was killed immediately. In 1981 I taught myself BASIC and wrote a program to paint pictures, then one that allowed animation.

Meeting Kate was serendipity. I had already noticed her and being shy I'd never said anything, but when I went freelance and put an advert in the paper for another designer, she came for an interview. I liked her diverse background. It wasn't a casting couch, either; I hired her purely on ability, and her analytical approach to art matched mine.

Foolishly, Kate gave me her house key when she went away, and asked me to look after the cat. I thought the best way would be 24-hour attention. Kate was obviously over the moon when she returned. I always err on the side of caution but my sole exception was moving in with Kate.

From my point of view the relationship has always been a smooth ride, but the company was a different thing. I knew printing was going to go electronic and that we needed to make an investment in equipment, so I went to see every bank manager in the area.

At the same time, we were snowed under with application forms for credit cards. Thefirms ask if you have mortgages or loans, but they don't ask if you have other credit cards, so we had a wonderful collection of them.

I was a member of this computer club in Birmingham and I picked up work converting American games for UK machines, and the multi-player game Gauntlet for the Atari.

I have always loved doodling, drawing and developing ideas for characters, but I draw the line is actual dialogue. Kate is very good at dialect.

The game that went ballistic was Corporation in 1989. We had a bidding war between three US publishers. We have since focused on developing story-based games, with an emotional and conversational interface, because that appeals across the family. People see games as a male bastion, but 40 per cent of the audience is female.

In 1995 the games industry hit its worst depression. Things were becoming bleaker and bleaker but Kate is great under pressure. She doesn't suffer fools gladly and can be quite direct.

As the public face of the company, I was getting a lot of job offers, and the fact that we could close the company down and I could take a higher-paid job elsewhere gave us comfort.

That same year, we decided to diversify but we knew that to grow the company we couldn't both be creative. Kate made the sacrifice and stepped away to focus on the company. It was the best thing we have done.

We diversified into music, broadcast and production and quickly had to become credible. I said to Kate: "Go get 'em", which she did. She cold-called and went to meetings, and because we both have an infinite amount of belief in what we do, that made it easier.

The internet is probably our biggest challenge. For Astro Knights, I have been putting the tools in place that work equally well for interactive TV as for other media.

Kate has been determined to break down the walls. She is persistent and if she believes something works, she will go for it. Whatever curve ball people throw at her, she's able to refute it. I find it very frustrating selling someone else on a thought process, but Kate is wonderful at that.