Until a month ago he was a school teacher in north Devon. But for the past 18 months he has been "dabbling" in selling newly built French apartments, houses and chalets after forging links with developers across the Channel.
He is one of a small number of British agents dealing with sale-and-leaseback properties - flats in ski, beach or golf resorts that offer buyers guaranteed rental income.
However, Borthwick is not a fan of his new colleagues. His website, www.frenchbuy2let.com, describes rival agents offering 15 per cent discounts as "fly- by-night" and of being left in the dark when he bought homes in France. Yet he says despite being a newcomer, his selling point is experience.
"Most other British agents selling in France don't own anything there but I'm about to buy my fifth place. Very few visit one development they sell but I go to all of them," he says.
"Most agents accept information from developers without checking but I analyse contracts," he says. As a result, he rejects two out of three developments.
Borthwick cut his business teeth organising share clubs for colleagues during his 12 years as a teacher before reading about sale-and-leaseback in 2001.
He does not have an office, preferring to trade from his Devon home. Borthwick's fees depend on the value of the sale and he uses budget flights to visit developments. He admits that this way of working means that although his holidays are shorter, his pay is better. His business cost £10,000 to set up but has earned him a six-figure profit in its first year.
There are pros and cons to sale-and-leaseback
A buyer has to select specific weeks of the year for personal use of the property but then must lease it back to the developer in return for a guaranteed annual rent - usually 5 per cent of the purchase price - which should cover the low-cost euro mortgages that Borthwick advises. "You can easily borrow at 3 per cent or 3.5 per cent, and even a 20-year fixed rate mortgage is only 4.5 per cent, so your running costs are covered by the guaranteed rent," he says.
A disadvantage is that owners are normally locked in to deals for at least 10 years, and the purchase price is often thought to be inflated. However, once a buyer sells, he should benefit from the capital appreciation.
"It's got more potential than the UK housing market right now. French house prices have risen 3 per cent to 4 per cent per annum for many years, then shot up 10 per cent to 12 per cent in the past couple of years. Someone buying now may well double the value of a home within five years," he says.
Typical of the properties he sells are two bedroom log-cabin style villas at Lecanau in the heart of the French wine region of the Médoc peninsula. The resort has a 14km beach, a lake and a pine forest nearby. Prices are from about £118,000 and there is an index-linked 5.3 per cent guaranteed rental income.
Near the ski slopes of Chamrousse, Borthwick can supply two-bedroom apartments from about £80,000 and four-bedroom ones for £160,000, usually with 80 per cent mortgages.
Borthwick himself owns a ski chalet near Courcheval, a studio flat in Nantes, a derelict barn awaiting renovation in Normandy and an apartment close to St Tropez. He is now awaiting acceptance of his offer on another flat near Montpelier. If the deal goes through it will take his portfolio's value to more than €500,000 with most involving leaseback deals.
"I've always been interested in investment but never thought I'd do it as a full-time job. I'm a bit of an anorak about it all now but I think I've got the right recipe to help buyers. Leaseback is relatively unknown in the UK but it deserves a wider audience," he says, sounding like a veteran estate agent already.
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