Hi , apologies , I’m sure this scenario has been asked and answered numerous times

..Id previously booked LHR-SIN in F in June

I originally intended to travel to London the day before by train from the NW of England , relax overnight in Central London , however , with high hotel prices in June that’s now becoming less attractive and I’m looking at alternatives , including a flight from Manchester on the day of my long haul

I presume any Man-LHR flight would be a separate booking and can’t now be linked , meaning my LHR-SIN wasn’t protected if there was delays at Manchester?

Would BA at MAN book my bag(s) through to SIN , or would I have to collect them at LHR?

Many Thanks