For sale: one Chelsea tattoo - hardly used. My arm doesn't like me; I made it suffer for my art. I had the tattoo done a year ago, to make myself look more acceptable to the Chelsea Head Hunters - the gang of football hooligans I infiltrated for my new BBC series, MacIntyre Undercover. So the time has come to peel that skin and get rid of the tattoo.

A friend asks if the BBC are going to pay. I hadn't thought of that. Maybe they'll only pay to replace it with the BBC logo or an advert for Radio 5 Live. The series has cost and arm and a leg, the accountant told me. I took it to mean that he wanted another logo on my thigh.

Many people think the tattoo was a step too far, including my mum. I suppose I have to agree. But, as an Irish Catholic BBC journalist trying to blend into a group of English nationalist violence-loving trouble-makers, I had a lot to cover up.

Women flooded into the Manchester tattoo parlour and I waited my turn as they endured their ordeal with poise and coffee-table grace. I went white. I went green. I fainted. I thought I was going to die. Physically sick. It reminded me of the time I nearly drowned as a young canoeist. I was trapped under water and could not get out of my boat. For two minutes I struggled for breath and eventually fell unconscious and went limp and escaped. There has been no escape from the tattoo over the past year. But I promise myself my Christmas present to myself this year will be the removal of the tattoo. I will pay.

n

ON TUESDAY, as 18 months' work on the series come to an end, thoughts come flooding back. For 32 years I have shared Christmas with my family but last year I had a new family. Last Christmas Day I worked in a care home for the second programme in the Undercover series. It was a home for people with learning difficulties. I hope I was family to them - they were certainly family to me.

Tears well up as I think of the awful things I've witnessed and heard over the past year. The things I've seen I never want to see or hear again. These things can pollute you and can be corrosive. I never want to become unshockable. From the dark heart of the fashion industry to the distress of a care home - it's all overwhelming. On the eve of broadcast of the first programme in the series, I'm in a BBC safe house for my security and have rushed home to see the last episode of Walking With Dinosaurs. I find myself seeking refuge in quieter, gentler places.

n

STILL TUESDAY. My new series goes out tonight. I spend the day doing interviews at Television Centre. In the early evening we (the team) gather for a drink in the BBC bar. I've thanked them for their unbelievable generosity - for their forgiveness of all my moods and frustrations. Disturbingly, there are no signs of dissent. It's been a tough journey for the whole team. Later, when I see the programme go out, I can barely watch it. I wince at every word of commentary and recoil at the views I have to acquiesce to while undercover with the Chelsea Head Hunters.

My family call me. I have been an awful son and brother and worse friend, and shortly I will have to make recompense. With relish. As the credits roll I know that this is the last undercover work that I am likely to do. For the first time during the broadcast I smile.

n

IT'S THURSDAY and hooligans on the web have begun to voice their views. "Fancy letting a f---ing Irish scummer into your mob like that." Another wrote: "Still can't get over seeing that c--- flat out on the table. Don't worry, there's a lot of game boys coming up your end to put your fearlessness to the test."

This very day last year I remember meeting my nephew. He is five years old. Whenever I see him he asks me to tell him stories. They must have certain ingredients. They must have three bits of danger, a big monster and a long journey. I thought at the time, bloody hell, next he'll be asking for audience figures.

This afternoon I finally make it back to my desk. And on my desk there's a note. It's from Peter Salmon's assistant. The channel controller wants to see me next week. I hope he hasn't been speaking to my nephew.

n

FRIDAY STARTS in a sound studio. I am doing the voice-over for one of the later programmes. By-passing stutters and slips I struggle through, repeating and stopping at every paragraph of commentary. In every voice- over there is always one word or phrase that is beyond me - on the first programme it was "Head Hunters". Those aitches! On a programme about hooligans that's a real problem. I can just about manage "undercover" without hesitation - I'd never survive on Just A Minute.

The first programme has gone out this week, but it's only the beginning. Next week I'll have transformed from a hooligan into a care-worker; the week after that I'll be a fashion photographer, then a fraudster, then an insider dealer ... Then and only then, finally, after 18 months - I'll be Donal MacInytre again.

`MacIntyre Undercover' is on BBC1 on Tuesdays at 9.30pm.