It is difficult to say exactly what is going on from the photo and data alone....
That being said the thing I would worry about the most would be an infection below your skin called cellulitis.
If this is what is going on then it would be important to get started on antibiotics sooner rather than later...
It might also be an allergic reaction to something.
So. What should you do?
Given that this is Sunday it would not be unreasonable for you to go to A&E if for no other reason then to make sure this is not a case of cellulitis which, as I stated, can bet a lot worse quickly.
If you don't want to do go to A&E then I'd make sure your GP has a look at you tomorrow morning (I know....tough to do in the NHS :(
Does this make sense to you?
I am happy to be able to help you today. If you would be so kind, please help me get credit for my efforts in answering your questions and press the excellent feedback button for this encounter. And, don’t forget, I work for tips. I would also be happy to continue to answer any more questions you have until we have resolved your concern.
Dr. Rick MD FACS