If you go onto reduced pay due to sick leave you and your employer have to pay the contributions due on your full pay.
If this would cause hardship to you, you can write to the Pensions Office and ask for your contributions to be suspended until you return to work.
If you go onto unpaid sick leave neither you nor your employer will pay any contributions. When you return you will have the opportunity to pay the contributions you would have paid if you had been working normally. You would also have to pay the employer contributions if your employer does not wish to do so.