Given that he’s looking to earn 2.5% of your £30m budget once you’ve completed on the deal, you expect him to have found just what you want. You don’t expect to be told you have to compromise.

But even for £30m, you can’t always get what you want. For a start, you’ve got competition from the increasing number of buyers in your league — Americans, Indians, Russians and Middle Eastern clients, attracted by a favourable tax structure, good schools and a feeling that they’re safer in London than other important world cities. Last week The Sunday Times revealed that Oleg Deripaska, one of Russia’s richest oligarchs, had paid £25m for a Grade I-listed Regency house in Belgrave Square.

“People from abroad have fixed ideas, and what they want often doesn’t exist,” explains Robert Bailey of The Buying Solution, the property-finding department of the upmarket estate agent Knight Frank. “At least not in Mayfair or Belgravia or Kensington.” There are private roads in Hampstead and plenty of grand detached houses in St John’s Wood, but those areas are beyond the pale for this particular client, a Canadian oil magnate.

There’s a £27m house in Eaton Square that you’d think might just be good enough. It’s end-of-terrace — so semi rather than detached — but it does have an 87ft “enfilade” suite of reception rooms. Even so, the London base of the mega-rich socialite Lily Safra is not, says Bailey, an “absolutely perfect package”. You see, you have to step from your car onto the kerb and walk across the pavement to the front door — an arrangement that will have your security advisers shaking their heads.

What his rich clients want, says Bailey, is to be able to drive into a secure garage, at the back of the house or underground, and not have to emerge from their car onto the public street. “Perfection is Belgravia with an integral garage.”

So what about Andrew Lloyd Webber’s old place on Eaton Square, with its integral mews — at £16.5m? Oh dear — it’s mid-terrace, and it’s on five floors. “My man wants lateral,” Bailey says.

Not easy to find. It was reported last week that its Norwegian owner wanted to sell The Old Rectory in Chelsea for £100m. The house is “detached with a secure perimeter, a real trophy house”, says Ed Mead of estate agency Douglas & Gordon — but he and Bailey dismiss the rumours that it’s on the market.

A few years ago Bailey rather cleverly acquired the lodge next door to 15 Kensington Palace Gardens (the area’s only private road) for the Crown Estate, creating a secure compound. “Without that it would have been flawed,” says Bailey. As it was, three buyers competed for it and it sold for more than £50m six months ago.

There’s an 18,000sq ft house in Melbury Road, Holland Park, its garages tucked away behind tall metal gates, for a mere £13.5m, but it’s “blighted”: the large garden is overlooked by a block of flats. “It’s a lot of house for the money, but it’s not good enough for my man.”

Some demands take only money to be met. “The ‘toys’ can all be put in — the pool, the media room, the home spa and treatment room, the lift — very important for moving luggage, these people travel a lot,” explains Bailey. But a one-acre garden in the centre of town is not so easily come by.

There’s a standalone Chelsea house with its own tennis court, but that’s probably “not grand enough for my client”, he sighs. Anyway, it’s not for sale. Not yet, at least.

For after inspecting the available properties that come close to his client’s wish list, and deciding they don’t come close enough, Bailey will start on the unavailable ones.

“I’ll identify houses he would want and talk to the owners,” he explains. “People who bought these kind of houses four or five years ago for about £15m are sitting on a gold mine. And it can be music to their ears when they’re offered more and more — if it’s pushed high enough, they’ll sell.”

The Buying Solution, 020 7861 1097, www.thebuyingsolution.co.uk

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