Some folks don't change their passport to reflect their married name until the passport need renewing... no problem at all with UKBA.

And some women don't ever change their name. In Spain by law they cannot do so and in UK they can choose whether to or not. In fact there is no UK law which says they can change their name but equally there is no law which says they cannot, that most do, is just a custom, supported by Common Law.

Thus it is not a UK legal requirement for a woman to change her name on marriage. As Terpe says, the marriage cert confirms her married status.