If anyone is sending heavy or very bulky but quite light (less than 5kg) then TNT provide some great services for next day for under £9 via parcel2go
Even heavier parcels don't cost that much with them, I sent a 26kg item last week with them that was out of most couriers weight and size limits, it only cost me £40 and £15 of that was for extra insurance due to item value of £478
Myhermes offer a great service, and I've had 1 claim with them for damage and they have just accepted this claim (took 30 days to get them to accept the claim)