certificate of lawful development

HMO Licensing

Ive searched back through past posts and there is quite a lot of general info posted however as this make or break wanted to get views & any ideas I can please.

We completed on our 1st hmo last year. Previous landlord cancelled his license so council sent us the application within a day or so. I completed this quite recently and very swiftly get a tug from planning to state no appropriate planning in place etc etc so apply or stop.

Keeping in mind that bit green & new to hmo I was semi prepared for this (I had asked & Agent had originally informed had c4 planning, council next to impossible to check with at time as could not visit during restrictions phoning useless. I also asked conveyancing solicitor to check on agreeing a deal etc)

Things progress with restrictions & lockdown as a backgroud & I asked again; solicitor informs seller has license so all ok that C4 not really relevant etc etc -
I scratch my head & asked for previous years AST's which arrive.
With sols advice I made judgment that reasonably safe. (My mistake)

I have approached planning consultants who will charge a bomb but are confidant can secure permissions I tried phoning planning to ask do i just send in proof (4+++ years tenancy agreements + safety certs etc etc) and we are done but not available still.
Not Sui Generis and we are A4 area.
My thoughts are to go with the consultants & get it done.

Cut to this year and if not lawful (tenants agreed till end 2022) I have major problem - any thoughts or input gratefully received ?