If additional works are carried out before a compensation event is assessed, is the contractor paid a reasonable sum in the next assessment?
Depends which option you are working under. If it is a cost reimbursible option e.g. option C, then you are paid all actual costs incurred so any works done will be payable if you can prove you have incurred them and they are not dis-allowable.
Option A however you are paid for completed activities on the activity schedule, and a CE does not make the activity schedule until they are implemented. Therefore there is no way for you to be paid on account - and if they choose to it will be purely at their discretion (but no obligation). It is another reason why you should try to get through the CE process as quick as possible so that they get to be implemented.
It depends on what Main Option you are using.
If option A (priced contract with activity schedule) or option B (priced contract with bill of quantities), then payment is made against implemented CE’s only, as they are then added to the activity schedule or bill of quantities, respectively, which is the document used to assess interim payments.
For option C (target cost with activity schedule), option D (target cost with bill of quantities) or option E (cost reimbursable) then the payment mechanism is based on ‘actual’ cost, so would include any costs expended against CE’s whether they are implemented or not, as the CE assessment is used to adjust the target or budget (Prices).