The 1.8 has probably been the most defined engine in terms of tuning. A remap you are talking around £400 - 700
LR/Rover/MG
pre 2001
1.8 118bhp (MEMS 1.9) - Re-map on standard ECU not possible, Aftermarket only
pre 2001
1.8VVC 145bhp (MEMS 2J) - Re-map on standard ECU not possible, Aftermarket only
2001 onwards 1.8 115bhp / 1.8VVC 145bhp (MEMS 3) - Re-map possible on standard ECU
Not to mention Lotus took the ECU one step further and did their own fancy tuning to it. You could always install a Lotus ECU.
If you are going for an after market chip then Emerald seem to get good press in the MG-Rover.org forum.
You will only get 5% increase in power from a re-map on aspirated engines, not much power for your money. Different story for Turbo charged engines. There is a turbo charged k-series at £5000

churning out 220 bhp.
Worst thing is it only knocks off a second for 0-60 time on the VVC models to 6 seconds.
Better to get the head ports re-worked, bigger valves, individual throttle bodies, agressive Cams etc