My initial impression is that TOW is quite heavy for EGLC, and flap 18 is quite a low flap setting.
I just set up a basic EGLC-LSZH flight plan on Simbrief with the RJ100, and opened the Takeoff Performance calculator. For EGLC, it has given me a maximum runway weight of 40,100kg and a Flap 30 takeoff at that weight. That is also with TOGA MAX selected on the TRP.
For reference, some airlines would actually takeoff from EGLC with Flap 33 selected! Quite the unique quirk of the RJ.
Mark - Just Flight