I've been quoted £426 all in for my 90k Service on an 07 plate TD4 with an extra £54.00 for the MOT.

If I go to my local indy will my LR select warranty be affected and will the £750 mot failure warranty still be honored if the car fails???

Sounds like the same price I just paid at Guy Salmon, Knutsford for the 90k service on my 2007/57 - bit of a shame it only has 38k on the clock. Watch out though - with mine, as it is just 6 years old they rang me 90 mins after drop-off to say it needed a brake fluid change (every 3 years) at £71. I agreed but when I collected I complained as to why ths hadn't been mentioned at booking-in on the phone time as the increased price may have prompted me to shop around. In the event they waived the charge for the brake fluid change.
Next year I'm likely to go back to the Indie I used for my previous 2 LRs. FL2 2007 57 GS
D2 2005 Td5 - gone and not missed
FL1 2005 Td4 - gone and missed

Copley LR are charging me £33 labour for brake fluid change , I am supplying all oils .