Just to answer the question in slightly simpler terms (CAP, credit, TASS and NCP are not things anybody outside of BA will understand)...
- S/H has tours of up to 5 days; each month you can bid for the work you want and even at the bottom of the seniority list achieve plenty of 2,3 and 4 day trips. However, work on having at least a couple of day trips every month. If you don’t live within easy driving distance you will need accommodation of some sort near LHR a few nights every month between trips.
- LGW is different, mostly day trips for everybody. You need to live within easy commuting distance.
- Overtime is available; at LHR it is all electronic...log in to the online rostering system, if you see a trip which fits on your line legally then you can pick it up and generally be paid overtime for it. I say generally, because there are a few health warnings to go with it; complicated, but essentially if you didn’t already have your full monthly work commitment on your roster then additional work just plugs the gap and doesn’t get paid as overtime. Best understood (sadly) by getting it wrong in your early days - the system has lots of intricacies and catches out the most experienced guys. Top tip - once training complete, chat to skippers over a beer down route and you’ll pick it up gradually! The value of the trip depends on numerous factors, but largely how many flying hours it contains and what your paypoint is.
- Overtime at LGW is not electronic. You can ring up to volunteer days in advance, or alternatively wait for desperate text messages for uncovered work on the day and then ring up. FOs get paid a flat rate of £514.33 per day (before tax), two days payable if the trip goes over midnight so can be very lucrative for an easy 2-sector late.
I hope that helps to give a broad overview - I would stress once again that the bidding system is complicated and best learned about gradually once line training finished!