Remortgaging - is there any advantage of delaying completion date to the end of the month?

[OhOneOhTwoOhThree]

Hello. I've had a nose around and can't see any other threads asking this question.

I'm in the middle of remortgaging with the Halifax. They are treating it as a fresh application (rather than the product switches I've done before over the phone), so there is conveyancing being done.

I have had to fill in a questionnaire for the conveyancers, who have asked whether I want to delay completion to the end of the month. I can't work out if there is any advantage to doing so - can any wiser mumsnetters advise please? My current mortgage payment goes out on the first of the month, so would I end up having to pay twice if the completion is mid month?

The saving is quite significant, so I'm keen to take advantage of it asap

TIA

?????
why would you pay twice?
interest is calculated daily

I'm having brain block. When I've switched products before the replacement product has just kicked in as soon as the old one finished and there hasn't been any conveyancing. This time, because it's being treated as a new mortgage I'm being asked for a completion date, and whether I want it to be delayed to the end of the month.

So a payment will go out on 1 March (for the sake of argument) for the month of March. If we complete on 16 March (for the sake of argument) what happens?

the amount transferred to the new account will reduce

We are also remortgaging to the Halifax (new customers) and had the same option. We've stuck with the new mortgage payment being taken out on the 1st April rather than delaying, but our current lender (yorkshire bs) has said that we can phone in mid March and change the current mortgage payment date until after completion, this will be to make sure that the mortgage direct debit isn't taken on the 1st as this will cause the money to go out twice to two different lenders.

Thank you for replying Talkin.

Hope yours goes through smoothly Vada