screws holding wheel arch insert

I am having a session getting some of the jobs done on my Disco. Next is sorting out the headlight washers but I need to get access to the pump which means removing the plastic inserts inside the wheel arch.

I have undone 4 of the philips screws but the rest are solid. I sprayed wd40 earlier in the week but it hasn't helped.

I am concerned about rounding off these screws, does anyone have any suggestions as to how to undo them?

Failing that any suggestions on how to get them out?

isnt the pump on the bottom of the tank?
i cant see which plastic inserts you talking about!

Yes the pump is at the bottom of the tank but it is at the front. I have been able to get to the pump at the rear of the tank and have sorted out my rear wash wipe but I can't get access to the headlamp washer pump.

According to Rave I need to remove the front bumper but to do so I need to remove the wheel arch liner (which I think I called inserts) and it is the philips screws holding the liner in place that are causing the problem. They wont budge.

Pirahna screw remover tool in a very slow drill/grind off heads and remove shafts with molegrips/get a hacksaw blade behind them/cut a slot in and use a bloody big flathead screwdriver/drill them out with a big bit so only the outer ring is left of the head/........possibilities are endless.As usual,easy to say,harder to do.Good luck mate!