Replace G24q-1 (4-pins) with a B22 Bayonet
G24q-1 bulbs do not take mains voltage

I agree that the 8-terminal block is the standard UK mains splice. However, there must be a ballast or driver circuit between the mains connection and the G24q socket.  

You must account for that before you can rewire.  

My concern is that they may simply be using common UK wiring kit to extend from an external ballast to this location.  That would be reasonable to do if they use a ballast that can support 2+ lamps.  

This is an incandescent socket. Be careful!

A basic tenet of design is that fixtures not made for incandescents must not have sockets which could possibly take incandescents.  

Even if you are enlightened enough to use efficient LEDs, the person who comes after you may slap in an incandescent.   At that point, the bulb is making much more heat than the fixture was ever designed to accommodate, and you can start a fire. 

The bayonet socket you want to install will take incandescents.   

I can't see the rest of the fixture,  but make sure it is listed and rated for incandescents. 

If it is not, and  you want to fit LED bulbs, choose a socket type that only supports LEDs and not incandescents.  Or change to a fixture that is appropriate for incandescents.