No you can't assume. Check your contract, staff handbook or whatever. Most employers would say that your paid sick leave made up for losing the holiday. Some would allow you some or all of the holiday.
You can actualy claim payment for any untaken holidays during the current leave year that your sickness commences in, (I did some years ago). Once you are into a new holiday period, then you will no longer be able to claim for holidays, as you need to work in the year to acrue them. http://www.adviceguide.org.uk/
Check the CAB site for info.
You can be paid for current year holidays only if you are on half or no pay, ie the difference. You should not be paid the amount extra to your nomal pay.