Thanks Winglet747,
The advert wasn’t clear. I just assumed that BA were happy to start the new type rating on my EASA licence as per Conversion route 5, and the LST and CAA application forms would be enough to be hired. The UK CAA confirmed to me that as an ex Uk licence holder, I could do a new UK type rating on my EASA Licence and the LST would then ‘“open” my UK licence.