I work for a UK higher education institute, and have taken some photos for online & print (surgical procedures, labs, equipment etc)
Photography is not a part of my job description.
Who owns the images?
Usual disclaimer: I am not a lawyer. If the use of these images could potentially cause you a serious problem at work, talk to a lawyer in their professional capacity.
The best place to start is probably the UK copyright service's page on Photography and copyright; paragraph 1 is the crucial one here. This then comes down to whether the photos were taken "for the company" or whether it was a personal endeavour on your part. The sort of things that a court would look at here would include whether the photos were taken on company time, whether they were taken on company property and whether they were taken with company equipment - but that's not an exhaustive list, and none of those points will absolutely decide the matter one way or another.
I am not a lawyer, you should neither act nor refrain from acting on any advice I may offer.
That said, The Copyright, Designs and Patents Act 1988 is quite ambiguous in this situation since section 11 - First ownership of copyright says:-
(1) The author of a work is the first owner of any copyright in it, subject to the following provisions..
(2) Where a literary, dramatic, musical or artistic work [or a film] is made by an employee in the course of his employment, his employer is the first owner of any copyright in the work subject to any agreement to the contrary.
(3) This section does not apply to Crown copyright or Parliamentary copyright (see sections 163 and 165) or to copyright which subsists by virtue of section 168 (copyright of certain international organisations).
Since creating the image was/is not in the course of your employment (that is to say it was far outside your remit and job description) that there may be scope to assert yourself as the 'first owner'. That said, engaging in a legal battle with a higher education institution (which tend to have deep pockets especially for legal bills) may not be a useful application of your time and money. Depending on what you want to do with the images, you may be better off assessing the potential impact and operate on the basis that forgiveness is more readily obtainable than permission.
A lawyer will be able to research the precedents and give you a clearer answer as to how this law is interpreted in the courts.