Allocation of payments question

I have a question about allocation of payments in regards to promotional balances.

Currently I am looking at potentially taking advantage of 2 offers on one card, one for a money transfer offer and one for a balance transfer offer. It's a Barclaycard if that helps.

They have the same fee but different lengths of term so i'm wondering how a minimum payment would be applied to the balances.

Say theoretically i moved £2000 on the money transfer offer for 12 months and £1000 on the balance transfer offer for 18 months, gives a full balance of £3000 plus fees. I then make the required minimum payments monthly, how is that payment allocated to the 2 different offers.

There would be no other spending on the card.

thanks in advance.