we bought our dream house, which was a repossession, last year.
several things to consider:
you need to be in a position to move quickly between offer acceptance and completion - so preferably you wont be in a chain, and wont require a mortgage. we were not in a chain, but we did require a mortgage, so even if you aren't a cash buyer, all is not necessarily lost. but you do need to have advanced your mortgage application as far and as quickly as possible (i.e. you will need more than an offer "in principle"). i think it would be highly unlikely that your offer would be accepted by the bank if your purchase is dependent on selling your existing property.
regarding the offer level, its not just about what the bank will accept (although obviously that is the first hurdle) - its also about the offer being of a level sufficient to deter other buyers entering the game following the acceptance of your offer - when our offer was accepted, the marketing of the property was ramped up significantly, both on the internet, in local and national newspapers (including the sunday times) - the exact amount of our offer was publicized, and the offer was extended to interested parties "to submit higher offers prior to completion". if other people are interested (and this may include property developers), and they think you are getting the property at a steal, they may be tempted to throw in an offer to try their luck.
so essentially the property is likely to remain on the market until such time as you exchange contracts, meaning anyone can come in with a higher offer until that time - this explains the need to rush to exchange. it also means you will need to spend on things like survey, searches etc, all of which will be "at risk", as you could lose the property to another buyer right up till exchange.
you are unlikely to get very much information on the history of the property, and problems associated with it, so again, you will be buying "as seen", and will have limted/no recourse, if problems emerge once you have completed.
you will need to instruct a solicitor who you are VERY confident will be fast and responsive - this may be far more challenging than it seems. i was lucky, but i still spoke to my solicitor at least daily, sometimes multiple times a day...and running between mortgage lender, solicitor, home valuation agent, surveyor etc became my entire life for the 3 weeks between offer acceptance and exchange.
bottom line, you will need nerves of steal, and you will need to play a very active "project management" role in speeding all involved parties along.
however, that said, if you are successful, you may well end up getting the house of your dreams, at a fraction of the price it would be under a private seller (we bought ours for less than 50% of the listing price it had before it was repossessed).
good luck, and remember: nothing ventured, nothing gained!