According to a statement on the link if you pay using the 2 installments you have to pay an extra 4% which goes with the first payment. So in total you pay £9360 split £4860 and £4500.
Here is the section:
'All self-funded students whose sessional fee exceeds £2,000 have the option to pay by two instalments with the first instalment due on the latter of 1 September or 30 days from the date of the invoice and the second instalment due on 15 February. Please note that paying by instalments will incur a facility charge of 4% of the total fee for the year with this instalment charge payable with the first instalment.'