If you are an employee earning over £107pw you should qualify for SMP which as a small employer is entirely funded by the taxpayer.
If the business converts to a partnership (I assume your DP is currently a sole trader) with you and your DP as partners you will be able to work in the business and receive a share of the profit. This will affect your tax credits, although presumably not a lot as the overall amount of income coming in is not going to change.
Whether this is a good idea or not depends on a number of factors; you would need to go through the whole situation with an accountant to have a clearer idea.
Good or bad idea? My DP owns the business, has done for 12 years, I have always worked there in some capacity (doing accounts from home- unpaid) but have also worked full time in other jobs to bring in extra cash.
I officially went on the books and quit my full time job after the birth of my DS who has been quite poorly to give us flexibility re hospital admissions ect, I work 16 hours per week. I am now 26 wks pregnant and we are considering making me partner in the business. I have no idea where I stand when in comes to maternity pay ect. If I do not qualify then I will still take a wage from the business but is this even legal when I'm not working??? Not.a.clue! Will it affect any working tax credits ect (not that we get much anyway!)