Education pricing and installments

I'm a student planning on buying a MacBook Air for university. I verified with UniDays and qualify for the education pricing (roughly £100 cheaper), and wanted to also pay it off in monthly instalments to avoid a huge chunk of money coming out in one go.

However, when I come to payment options at the checkout, there seems to be no option for paying in instalments? The only option is to pay in full. I wanted to check if this was the same case without the education discount, so I came off the education store and tried going through the checkout with the MacBook at normal pricing, and the option to pay in instalments is there.

Why is the option to pay in instalments not available when buying the MacBook Air with the educational discount? Is anyone else having this issue? As far as I'm aware you're still meant to be able to pay in instalments even with the education pricing.