This is what direct.gov says
"Sickness
In light of a recent European Court of Justice (ECJ) ruling, the following is applicable if you become ill during your holiday or just before you were due to take it. You can ask to convert the period of holiday concerned to sick leave and ask to take the missed annual leave at a later date.
You should follow the usual procedure for telling your employer you are ill (eg letting them know as soon as you can or providing medical certificates). If you are not sure what your normal process is check your employment contract, staff handbook, or intranet.
You may be unable to take all of your holiday entitlement within your leave year because of illness. In this case, the ECJ judgment also means you may be entitled to carry forward the entitlement you would otherwise lose to the next year.
If you need further guidance on this subject, please contact Acas for advice.
Acas (Advisory, Conciliation and Arbitration Service)"
http://www.direct.gov...dholidays/DG_10034711
It appears you may be able to carry it forward to the next year. ACAS can help you
As for pay? I really don't know, but again ACAS can help. You have been very lucky to get full pay for 6 months then half pay for another 6, well done your employer.
Do you have contact with Macmillan at all? They have excellent benefit advisor's who will know exactly what, if any, benefit you are entitled to now and in the future.
gl with returning to work