Replacing pendant light but reusing existing chock (UK)
You cannot use choc block (connector strip) inside the ceiling void or externally not covered by a ceiling rose.

If you want to remove the existing rose entirely I would suggest one of these

https://www.tlc-direct.co.uk/Products/TLCT101C.html

which will take the three existing cables on the 'socket' part, provides a loop terminal for the live (the 3 brown wires) and the 'plug' part will connect to your new pendant (live, neutral and earth if needed). It has cable clamps on all the cables and can safely be poked back inside the ceiling void. 

Alternative is to remove the ceiling rose, hook and connector strip off the ikea pendant and wire it into the existing ceiling rose, threading the flex through the white rose cover before connecting, then screwing on the rose cover. 

For anyone not familiar with UK loop-in wiring, the top 3 blue wires are neutral, the middle 3 brown wires are live, and the bottom pair is (blue sleeved brown) switched live and (brown) live to the pendant.