Costs involved in splitting a house into flats...?

I've seen a property which has potential to split into 2 flats. A studio flat downstairs and a one bed upstairs.

Rent on the property would go from £600pm to £800-£850pm. Plus with bedroom tax kicking in I think there will be a big spike in demand for 1 bed properties.

I havn't got experience with this and would like to cost it up to work out if its worth it. This is a list of what I think would be involved:

- Adding an internal door at the top/bottom of the stairs to split the upstairs flat
- Sound deadening + tests - any ideas on costs?
- Approval from local planning department? - where do I start?
- Approval from building regulations? - where do I start?
- Fitting a kitchen upstairs - appart from the cost of the plumbing and units are there any other costs? gas regs?
- Fitting a bathroom downstairs - again, apart from plumbing and the suite itself are there any other costs?

My estimate is that this will be in the region of £3-£5k?

Can anybody share any knowledge on the costs/complications of this?

Thanks :)