STEPPING into the grand rooms of the Old Rectory in Chelsea you feel yourself shrinking - like Alice after she had drunk from the magic bottle. The ceilings are so high, the windows so vast, the scale so unlike the London streets outside.

It has been called a country house in London because of its setting in two-and-a-half acres of gardens. It's not just the size - though at 30,000 sq ft it is roughly as big as 30 three-bedroom semis. It is that the house has been conceived for the way the richest people live. And at pounds 25m it is Britain's most expensive house.

The central section of the front wall, just off the King's Road, dates from 1720 when the house was built as a rectory to Chelsea village church. As a boy, Charles Kingsley lived there. Fragments of the original interior remain, including two cast-iron fireplaces.

Such historical authenticity gives the house an extra cachet, but the class comes from the bold new wings. Sweeping round to the north are the vast reception rooms designed for regal levels of entertaining. The dining room has a colonnaded walk; the kitchen is fitted with industrial-quality aluminium and pewter equipment, designed to cater for parties of up to 100.

But it is the grandest of the entertaining rooms which reduces you to Alice size. The wing finishes with a spectacular 30ft cubed room, whose vast windows and domed ceiling give it the feeling of a summer pavilion.

The sweep of the south wing includes a 50ft swimming pool in a conservatory-style setting, with black, granite-studded tiles lining its base. Underneath is a gym and dance room - used as the setting for Elton John's next album cover.

Charles Ellingworth, of Property Vision, thinks the future owner is most likely to come from the Middle East: 'I don't think pounds 25m is way out of court if you compare it with other houses in London which have sold for pounds 5m or pounds 6m.'

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