Basically agree with the above reply, you can claim for these things, but it has to be in proportion.
For things like your phone that percentage is going to be low, we all use one for business but for a small, one man outfit it isn't a big overhead is it?
As for claiming for your flat/house;
Claim the cost of one room for office use.
So if you have 8 rooms in your house or flat you can reasonably claim one eighth of your household costs.
ten rooms then just a tenth and so on.....not sure about a one room bedsit though
Heating, electric, council tax and so on.
If you put a percentage of your mortgage against tax then you can be liable to capital gains as Shiner has said...don't think I would recommend that!
For a real answer you need to ask an accountant.
Ian