leak at the top of tap fitting on our a monobloc mixer tap?

I have leak at the top of tap fitting on our a monobloc mixer tap.
It works by lifting (tilting back) a handle on the top and turning the handle to either the left or right to control the heat of the water. The problem is, when it is turned off it leaks from the top around the swivel part (i think).
I have managed to unscrew the handle and remove the small grub screw which was hidden inside behind the handle, but problem i have now is removing the top to access the cartridge, it seems very difficult to disamantle, is there anything else holding this top in place? or is it just a matter of some brute force (dont want to really damage the top).

Also the cold pressure is very high,is there any adjustment that could be made?

Any advice will be much appreciated.