If you book EI flights to Ireland and NI from MAN on ba.com they would be under BA codeshares and you would get TPs for those.

Otherwise if you are based around Manchester then yes probably doing a return MAN-LHR is the obvious option for the remaining TPs. You should be able to get a return for a bit less than £100, have a look at google flights and see which dates give you the cheapest fares.