In England, it is normally possible to defer jury service (i.e. postpone or delay it) provided you have a valid reason. Examples of valid reasons for deferral might be:
In my experience the courts are very reasonable about deferring jury service. They realise that people have pre-booked appointments and the last thing they want is jurors that are resentful about being there.
The form you receive with your jury service summons gives you the option of asking for a deferral. You need to explain why you are asking for a postponement and give dates within the next 12 months that you are available. If you can’t make any dates you need to state this on the form and probably provide some kind of evidence (e.g. medical certificate or letter from the university)
The following is an extract from the “Her Majesty’s Courts Service” document: Guidance for summoning officers when considering deferral and excusal application (Crown Copyright 2009)
Guidance for summoning officers when considering deferral and excusal applications1. Applications to be deferred or excused from jury service must be considered carefully, sympathetically and with regard to the individual circumstances of the applicant. It is important that officers dealing with such applications should adopt a policy that is both fair to the individual and consistent with the needs of the court, i.e. providing a representative jury. Officers should therefore not hesitate to refuse a request if no “good reason” is given.2. If good reason is shown why the person should not sit on the date they have been summoned, deferral should always be considered in the first instance. Excusal from jury service should be reserved only for those cases where the jury summoning officer is satisfied that it would be unreasonable to require the person to serve at any time within the following twelve months.3. When deferring jury service, the summoning officer must specify a new date of attendance, which should normally be within one year of the date of the summons. In deciding on the new date the times identified by the potential juror as being particularly inconvenient should be avoided wherever possible.