We have a 35 week programme that is included in the contract. Each month we apply for prelims against the access date and planned completion. We are 30 weeks into the 35 weeks. There are a number of delays which we are currently discussing. We believe they are employers risks they are claiming they are our own doing. The latest programme was accepted showing a duration of 50 weeks. They are now assessing our prelims as 30 out of 50. Not 30 out of 35. Surely the prelims should be assessed against the contracted dates and either LADs or compensating events pick up the remaining 15 weeks?
You have not said which option you are working on but I am guessing it is option A, as under option C (onwards) you are paid actual cost anyway. If it is option A, it depends on how you initially spread your prelims in the first place but either way should not give rise to the situation you as you are paid for completed items on the activity schedule, not on percentage complete of any item. If your job was 8 months long and your prelims for the project were say £80k, I would have had 8 monthly milestones of £10k for Jan, Feb, March etc. You can then claim that amount each month up to the initial 30 week contract period. As you then say, any extension beyond week 30 will be picked up in compensation events, or have to be swallowed by yourselves if it is your own delay (as well as being charged delay damages).
What you are suggesting is that you are being paid percentage complete for a single 30 week prelim bar which is not correct in the first place.
The other option would have been to spread the cost of prelims against activities on the activity schedule/programme and then as you complete items you would be picking up prelim costs as well.