I’ve paid for my holiday arrangements. Can my travel company still request a surcharge?

Yes, as long as their booking conditions allow them to surcharge and don't say that no increases will be made after full payment is made.

Surcharging refers to your travel company changing the price of your holiday after you have booked your arrangements.

They can only surcharge where the cost of gone up in respect of fuel, taxes or fees, or the exchange rate relevant to the holiday. If the surcharge exceeds 8% of the holiday cost, you can either accept an alternative holiday or cancel and have a refund of your monies.

Surcharges shouldn't be confused with additional charges that you may incur for changes to your booking such as amendments or additional services.