Can anybody tell me at what service interval the cambelt should be changed and What I should expect to pay if it needs doing on my next service?

Currently my sig has done just short of 80k miles its a 54 plate 1.9 cdti 150 and has had 3 service stamps. the first 2 with vauxhall and the 3rd at 70k by national (i think).

Can you tell me what the intervals for servicing are too plaese?