Is it common?
Is it universal?
In short, it depends on the company
In the general "Working world" in the UK, it's certainly very common to have fixed hours. eg 8:30-5 or 9-5:30 with 1 hour mandatory lunch, for a 37.5 hour working week.
That's definitely not a standard rule, though - it's common, but there are a lot of companies where it's no longer standard practice: particularly within the IT field, which tends to be one of the more progressive when it comes to "flexible working".
Note that UK law states workers have a right to a 20 minute break if working for more than 6 hours in a day, but it does not state you have to exercise that right.
In a similar vein to "Are fixed working hours common practice in the UK?", the answer is quite simply "Yes it's common, no it's not universal". Out of 6 companies I've worked for, only 1 had truly fixed working hours. The others all allowed at least some degree of flex in your working hours, and none would have any objection to me foregoing lunch in order to work a shorter "Arrive->Leave" day, as long as it did not affect my productivity