@nowaitaminute, the powers already exist, but councils are reluctant to use them because they're complex, and the courts are reluctant to grant them.
Back in the late 70s/early 1980s, the GLC used these powers quite a lot. If the homes were in good nick, they became council houses. If they weren't, they were leased or sold to housing co-operatives and housing associations (who had more funds) for refurbishment. Some were sold on under a "homesteading" scheme, where people who were in housing need but had no chance of getting a council place, bought them cheaply from the council, with a GLC mortgage, and did them up.
This how come some friends of mine managed to get a garden flat just round the corner from Holland Park for £8k in approx 1978/9. It was a wreck, but full of original features and had the potential to be fantastc.
I'd just make it a lot easier, eg if a house has been empty for a year or more, and isn't in the process of being renovated/subject to probate or divorce proceedings/awaiting a decision re planning or demolition, they can take ownership if the owner fails to challenge the application for a CPO within a few months of application.
If there' was a mortgage, and the CPO price exceeded the amount outstanding, then the mortgagee would get their dosh, same as they do in any sale. If it doesn't, then the mortgagee comes after the mortgagor for the balance. That would really make owners think twice about leaving properties empty.
I don't know how long you're allowed to leave a property empty with a BTL mortgage, but on all my residential mortgages there's been a condition that the property won't be left unoccupied for more than a certain period of time without the consent of the lender. I've no idead who easy it is to get permission, but an easier CPO process might make lenders rethink that.
Any thing that brings empty properties back into use is to be encouraged imo.