I am also in the uk and going through all that at the moment. The first and most important thing you need to do is find a safety assessor as your products need to have a safety assessment before you can legally sell them, this sounds like hard work but I use an assessor that sells special packages for certain types of products which allows you to use a whole range of ingredients. You would have to buy 2 different packages, 1 for melt and pour soaps and the other for bath products, the website is http://cosmeticsafetyassessment.com/
if you would like to take a look.
There is a large amount of paperwork when you start selling too, you need a Product Information File on each of your products even if they only vary slightly, for example if you use a different fragrance. You also need to keep a record of every batch you make. all this is again a legal requirement
Labelling is a headache, there are 24 different possible allergens in fragrance oils/essential oils which need to be listed on the ingredients if they appear in your products at a rate of 0.1% or more so you would have to calculate this. There are many other considerations legally also, for example Insurance, and if you are making the soaps at home to begin with then you need to check with your mortgage lender/Landlord that you can work from home in this way.
Phew I hope I haven't put you off, I find my work very rewarding and am starting to make a little money for myself, but nowhere near enough to support myself as yet. My biggest tip is once you have done all the legal bits, have a look at the Country Markets Website, they run markets all over the country and you can become a producer for them for 5p (not a typo!) which allows you to sell your stuff there, they take a 10% commission on everything you sell but it's a great way to get started. the only downfall is that some of the markets do not have a huge amount of customers so I would take a look around before commiting to anything.
Whereabouts are you in the UK? I am in South East London right on the outskirts
Hope all goes ok for you