Computer Misuse Act 1990 s1:
(1)A person is guilty of an offence if—
(a)he causes a computer to perform any function with intent to secure access to any program or data held in any computer, or to enable any such access to be secured;
(b)the access he intends to secure , or to enable to be secured, is unauthorised; and
(c)he knows at the time when he causes the computer to perform the function that that is the case.
Section (c) might be an issue, but a simple letter can easily sort that.