Around one in four people have some type of adverse credit from missed credit card payments to County Court Judgements (CCJ's) and these people can have a difficult time obtaining mortgages, even if their past financial problems are behind them. This is usually because serious financial problems like loan defaults and County Court Judgements remain on public record for up to 6 years.
The mortgage market, however, is fiercely competitive and there are definitely options available to people with adverse credit who wish to obtain a mortgage. No matter which lender you approach, even if they specialise in bad credit mortgages, you will still be seen as a higher risk to the lender. You should probably expect to pay slightly higher interest rates than those offered with standard mortgages and you may not be offered the types of introductory deals offered to other applicants.
Depending on the lender, you will still be subject to the usual processes that go with organising a mortgage. Your prospective lender will probably perform some kind of credit check or apply a credit scoring system, although not all do this. You may find that you won't be eligible for quite as big a home loan as someone with a good credit history and you need to look out for early redemption penalties, as on bad credit mortgages they can be rather high.