I am alive and have returned from the NHS walk in centre!
Doctor agreed that it was a very bad bruise, and surprisingly deep but felt it was just a serious bruise as I didn't have accompanying symptoms. He believes I've damaged adipose tissue which is the hardness which should resolve itself in a couple of weeks, if it doesn't I'm to go visit my GP as they may need to remove it surgically (?!) but other than I'm fine - yay!
I do have a general appointment with my GP next week, I'll keep a close eye on it and if it's not all gravy I'll raise it again then.
Thanks for all the advice and good wishes everybody.