Bee the thing is, and I recognise this will vary regionally, but certainly here, the difference between flats and houses and one bed and two beds don't really vary so very much.
I found a one bedroom flat on right move yesterday for £110,000. Less than three miles away was a three bedroom house for the same price. Now conceded, the flat was in a slightly more salubrious area, but still in that exact location you could get a lovely three bedroom house for less than £200,000. Split between two people, you'd be paying less than for the flat.
In other words, person A buys the one bedroom flat and has a mortgage of £100,000 so let's say £600 a month. She has to pay council tax of £84 p/m, gas, electricity, Internet and tv licence.
Couple B have splashed out a bit and have bought a three bedroom house down the road for £180,000 and they have a mortgage of £160,000. Their mortgage is obviously more than person A's and is £900 a month but split between the two of them that's £450 each.
So with a more desirable, roomy property it's STILL more expensive for A to live in a one bedroom flat.