In fact it is not all that big, but it has a very commanding presence. At 16 feet wide and 40 feet long, it's not that far off the dimensions of a standard London terraced house, but there the resemblance ends. This is a freestanding structure, a timber-clad cigar-box of a house, though it could also be described as an ambitious back extension to the large old building behind it, formerly a riverside hotel. Being where it is, however, everything is turned around. Here a strip of buildings including the old hotel fronts onto the river, and Mortlake High Street runs along behind. Consequently Big House is on the High Street, not the river.

Moreover, it is right next to a large new housing development which is not nearly so interesting. But none of this matters because Big House sits next to a big gap in the buildings where a broad alley goes down to the river. It has panoramic windows, it has a roof terrace, and because of the way the river curves round at this point - the final back-breaking curve for the Boat Race rowers - it gets an excellent view by effectively looking back over its shoulder.

Not that the view out the front is too bad, either, owing to the position of the rather nice St. Mary's church just across the street, dating back to the time of Henry VIII. This would once have been the centre of Mortlake village. There's something of a Tudor flavour round here, since Big House is on the site of the estate of Dr. John Dee, the Elizabethan magus who practised alchemy and the dark arts. In the 17th century it became part of a famous tapestry works. But in recent years the site had become run-down. Big house is built on what had become just the yard off the street behind the hotel.