Although I don’t advertise it, I do offer bookkeeping for a number of my clients (rather than accounting per say) and I do this with no formal training, so I would say that you could probably retain a few clients with your experience in accounting.
You do need to register with HMRC for MLR and it is currently £110 per year - better to register though as the fine is quite hefty if you don’t (I was fined £100 for registering late and also had to pay some back registration fees).
You then need to ensure you keep records of all the clients you have (much like the type you need when opening a bank account - picture id and utility bill etc) - details can be found here: soca.gov.uk/ if you see any underhand goings on with client finances!
I use Kashflow and Xero for most of my clients and we give access to accountants through both of these - I tend to input receipts/issue invoices/chase outstanding payments/set up payments in clients bank accounts (I have access to two client bank accounts to make payments) and do VAT returns for them. The accountants then do the year end reports. They also tend to do any payroll and forward to me each month for me to make payments to employees and the PAYE returns to HMRC.
Considering I was never going to get involved in figures I do spend quite a bit of time now on bookkeeping!