Millie, I guess you almost certainly have an Assured Shorthold Tenancy, which doesn't give a tenant much in the way of security of tenure (another one of Thatcher's big ideas to free up the housing market and make sure that they become a fantasitc investment for the rich, and out of reach for the poor - but that's a rant for another time). However, if push comes to shove, remember that you cannot be
made to leave without a court order, and these can take time and cost money to organise. You may be able to find some useful booklets explaining your rights
here.
If he has any sense, your LL should be game for a bit of serious negotiation - if he is selling to release capital, then £x,000 now could realistically be more useful to him than, say, £(x + 10),000 in six months time; selling to you will also avoid agent's fees. If he needs an early sale, and he doesn't sell to you, then he is limiting himself to a market of other landlords, or people who are prepared to do the legal work to force you out. This is limiting his options, and as no prospective LL will pay more than a certain multiple of the annual rental income (typically 10-20 times), then he may be restricting his price, too.
In terms of getting a mortgage, if you have any interest in buying, go and see about 20 financial advisers and mortgage brokers. Go right through the yellow pages if necessary. Find one who is
interested in your situation, and will take
your side in dealings with the lenders. In my experience, this can make a huge difference to what is possible in terms of raising money (in the past I visited dozens of brokers with a tale not dissimilar to yours - I finally found one who was
interested, and suddenly the impossible started to become possible). You may be able to work out a way to come up with the money, even if it is only in the short term, enabling you to sell the house at full value, and make a bit of a profit from your situation. Find out about 'non-status' and 'self certification' mortgages; these do not depend upon multiples of your income, you just need to be able to say you can meet the repayments. If your intention is to sell straight away, an interest-only mortgage may not be too foolish to consider, either.
)
Fingers crossed for you, wherever it is located!