Consider a 2 bed flat at £250,000 - London and the SE is full of them. Rental value is around £1,000 a month, which sounds as if it should mean £12,000 a year or not much short of 5%. But it doesn't. Subtract unoccupied periods and agents' fees and it is more like £10,000. Then go for more deductions - higher mortgage costs for buy to let, legitimate wear and tear, damage to the flat, possible legal costs - and you make a very big dent in that £10,000. And whatever you gross is taxable. Then you've got the problems of getting a tenant out if you decide to sell, and the sheer misery of dealing with problems the agent can't sort. It actually makes sense to leave a property empty.
If you have £250,000 sitting around then you have very boring saving returns (perhaps 1%) or the thrills of the stockmarket or high stakes gambling on the currency market - or stick it in a property for potential increase in property value. A modest 3% is way better than a savings account. 5% looks reasonable. Even 10% is credible. There are (small) patches in England which have seen upwards of 30% in the last 18 months, say 20% pa. And it is hard to see a slump of more than say 20% (which makes it a lot safer than the stock market).
Of course this leads to the scenario of empty flats - in effect the supply of homes is reduced.
As a rule of thumb, rental yeilds must be 130% of the mortgage payments, factor in the 25%deposit, stamp duty, solicitors fee's furnishings, then letting agents costs in the 1st year.
I cannot speak for London and the SE, but rental values generally everywhere else are 450-550 for a 2 bed, 550-650 for a 3 bed, and 650-750 for a 4 bed property. (of course you can get higher rents)
Anyone investing in property if they keep to these figures will get a return of 100% within 7 years regardless of so called housing crashes, burst bubbles etc.
OK finding property where the sums add up, is proving very difficult but there are distressed sellers out there, always have been always will be, also people looking for a quick sale. If you can buy a property 10-15% below market value, that will cover the initial costs.
Even if you have to sell within a year, you will make back your initial investment.
A lot of people went into the property buy-to-let market through property clubs and were conned and hurt, the buy to let market has on the whole got rid of these, this increased values of all properties, but now the buy to let market is actually helping in reducing the values of all properties back to a managable and affordable level.