VCAS5100 - Cash accounting scheme: Records and accounts: Discounts on VAT invoices
http://www.hmrc.gov.uk/manuals/vcasmanual/vcas5100.htm
If a prompt payment discount is offered,
VAT is chargeable on the discounted tax-exclusive invoiced price,
even if the customer does not take up the offer.
Value Added Tax Act 1994
http://www.legislation.gov.uk/ukpga/1994/23/schedule/6
4(1)Where goods or services are supplied for a consideration in money and on terms
allowing a discount for prompt payment,
the consideration shall be taken for the purposes of section 19 as reduced by the discount,
whether or not payment is made in accordance with those terms.
Therefore, the consideration for VAT purpose in your case is
£1,600*(1-0.25)*(1-0.05)=£1,140
VAT on the invoice is as follows
£1,140*VAT of 0.2=£228
.....Net........VAT......Consideration due
£1,200 + £228 =£1,428
VAT for invoices with early payment discounts
http://www.taxationweb.co.uk/forum/vat-for-invoices-with-early-payment-discounts-t27744.html
"Although this may make your supplies "cheaper" for non vat registered customer
- so there is some benefit here."
"The customer that does not take the discount is only entitled to reclaim vat on the discounted amount - if they are vat registered then their input vat claim will be lower."