1) I am planning on connecting the wiring to a fused spur with rcd in
the house. Will the length of the wire run cause a problem with the
rcd (do not want it tripping every 30 seconds)

If it does, there is a fault in the cabling (or final load).

2) Will I be able to use the one run of cable for both the lights and
the water pump or will I need to run two seperate cables.

Yes you can. However, if you want to be able to switch them from the house,
you'll need separate supplies for both.

To calculate the cable size, add up the total load. Then go to
www.tlc-direct.co.uk and find the cable you want and bring up the
information page. Somewhere you will find a link to the cable size
calculator. Put in the required details (i.e. 2 core SWA XLPE and 1000W) and
it will tell you what minimum cable size you need. The selection will
probably be voltage drop limited. You might consider trying 3120W, as this
will enable the full benefit of your RCD fused spur should you choose to
install an IP66 socket. You may wish to check the final calculation directly
against the regs.

BTW, I tried 3120W @ 240V with SWA XLPE 2 core, with 30m and it suggested
2.5mm. It uses a large proportion of the allowed voltage drop, so any long
runs inside the house may tip it over, requiring 4mm.

Christian.