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 this tech doc.
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.