Hi I have purchased a police Tickford cluster with extra 2 gauges (volts and oil) and swapping it from a standard gli cluster with only 4 gauges in total. I'm unsure whether I will need anything for the 2 new gauges to work. Any help appreciated.

Yes.
All the info you need is in {DESCRIPTION}
Make sure you get the correct oil pressure sender, NOT the switch as this only works for the oil pressure warning light. On the XH you'll need the round EF/L type.