Thanks for your reply.
As there has been no extension, planning permission would not have been required.
As regards ***** ***** this should have been obtained if you had knocked out any load bearing wall. Likewise, if you had added new plumbing or electrics, this work should have been given Building Regs by the appropriate installer.
From what you have said, and I am not a Building Control Officer, it does not appear that Building Regs would have been required for the alteration only may have been needed for the plumbing/electrics if applicable.
The 2 options you have are-
1. Obtain the advice of an independent Building Surveyor to see if Building Regs should have been obtained.
2. You do nothing, and as and when you sell, you can indeed offer a Building Regulations indemnity policy to your Buyer if the issue/query is raised over the shower room. Such a policy is quite cheap- £50-£100 depending on the value of your property and is a one off payment. A Policy can be issued and arranged by your Solicitor provided the work was done over 12 months ago (as you seem to be aware, the Council can only take enforcement action against you if the work has been done less than 12 months ago).
If you go for option 1, and it turns out Building Regs was required, you do of course run the risk of having to carry out remedial works if the Building Control Officer is not happy with the work in its current state.
I therefore have to leave it to you to decide which way you want to proceed.
I hope this assists and sets put the legal position. I must say, indemnity policies are very much a reasonable cheap solution which most clients rely on.
If I have helped, I would be grateful if you could rate my answer.