Am I allowed time off to attend a job interview?

Not normally. You will probably have to take it as annual leave, if your employer does not offer a flexi-time arrangement which would allow you to take some time out during the day. Of course, it might not be the best idea to let your employer know you're looking for other jobs by asking for time off for an interview in the first place.

Your employer may let you have time in certain circumstances, for example if the interview is for an internal vacancy, or if you are to be made redundant and they are helping you to look for another job. This would be entirely at their discretion though.