The straight answer is here
http://www.communitie...lations/publications/
From that site you can get to the various approved documents that comprise the Building Regulations for England and Wales. Scotland is similar but different, as is N Ireland, and I believe Wales will eventually be different (but all of them are very similar).
However this really isn't going to help you much because these are technical documents and it would take someone days to read them all. If you are just talking about shapes and sizes of rooms, most of what you require would be found in the document that deals with safety (which, for example, defines distances for doors opening out onto stairwells), the hygiene document (which would deal with washing facilities provision).
You'd be far better off talking to someone involved in building - could be a designer (for which you'd have to pay) or a tame builder (who might be willing to discuss the principles for a sniff of the eventual work contract), both of whom would have enough working knowledge of all the regs to know what the likely issues for your dwelling.
This is nothing to do with the Planning Department at the local authority - Building Control is different, and whilst you can ask them for general advice on how to move the project forward, they will not be able to provide you design guidance or be able to assess your project without drawings and a building control application (which costs around £300).
There is nothing that I know of that says a bedroom cannot open onto a living room - though it is not good practice.
Finally, creating an entirely separate flat is most likely to incur the property in being split into two for council tax assessment - so you need to think about whether this cost is what you w