You can, but it's not guaranteed you will be successful with this. The fact they haven't offered you the full amount is a good bargaining tool.
Send them a letter saying you will only accept this part settlement providing they pay you by cheque otherwise you will progress you claim for the full amount.
Remind them they have xx amount of days left as part of your prelim and if you don't hear from them then progress to your
lba
. If however, the deadline for the prelim has passed, then send your LBA for the full amount and on it say that you require payment by cheque.
I have been working closely with a guy with an RBS claim where we tried everything to get them to pay by cheque unfortunately it doesn't always work that way (we weren't successful).