If you want to see what a house worth over £70,000,000 looks like, take a look at this link from Rightmove. It's in Windlesham, Surrey and comes with 24 bedrooms, 11 acres, 5 (yes five) swimming pools, 2 outside, 2 inside and 1 on the roof. It also has tennis courts, an indoor squash court, a two-lane bowling alley, a cinema and stabling for 5 horses, plus of course it's own helipad. I could go on and on; the brochure is here.
On the opposite end of the spectrum I passed this site yesterday on my site visits, possibly the smallest house I have ever seen. The one on the end was up for sale through Village Estates Online whoever they are. Unfortunately, their website has ceased to exist and I would imagine so too has the company, although Companies House doesn't suggest so. From the state of the site it looks like it has been in this state for quite a while and I can't see too many investors jumping at the chance to snap this property up. Your options are hugely limited as to what you could do, what with the size and width more than anything of the property. As well as that it's in Homerton, great...
Updown Court is just around the corner from my house (which is obviously equally as magnificent). If I remember correctly it has never had a owner, despite being on the market for about 4 or 5 years. It has just sat there empty for all that time, I don't think there is anyone mad enough to buy it! I used to drive past it and dream though!