I think with the mortgage markets having tightened up a LOT over the last 4 years lots of people are renting until they can muster a 40% deposit (not exactly easy these days altho lots of young starters are being loaned the deposit by parents/grandparents).
I am currently in the process of buying my grandmothers house as a buy to let (2 bed semi) , looked at the price of the house and the money I need to spend on it to rent it and it comes out at a 6.6% Yield in the area where the house is. Thats roughly twice what I get for interest in my ISA's, if you dont need the money and you dont mind a bit of hassle its worth doing BTL for the long term.
You also need to consider housing market is still low and appreciation over the long term will likely increase the value substantially (My grandmothers house was valued 40% higher 3.5 years ago).
Advantages of BTL are potential increase in capital value, regular monthly income (at least while tenanted anyway lol), ability to offset maintenance and mortgage costs against rental income lowering tax liablity.
Disadvantages of BTL, not easy to get mortgage for them unless you ahve a decent deposit or proven record of buy to let market, paying tax on income above costs, costs to yourself if you cannot find a tenant. Dealing with estate agents, some want 15% of monthly rental for merely showing someone the house/flat etc and they do very little after that, best to do it yourself, even better if you have mates who are Sparks and Plumbers as they can sort potential issues for you.
Dont furnish a flat with nice things as they only get wrecked, cheap and cheerfull/replaceable is best bet, my best mate rents out 2 houses (in a pretty shonky area and the last 2 tenants in one of the houses took all the internal doors and the Boiler
, so now he puts cheap stuff in which is replaceable and he increased the deposit to cover cost of replacing the boiler twice over, so if they do take his boiler, he replaces it and pockets £1200 too (funny he does not mind if the current tenant takes the boiler)