Hotairlass,
is this the testing phase or the technical interview? If the technical interview, then they should be able to accomadate you (especially if you ask nicely) - otherwise you're best off to contact HR in Swawick. If you haven't had a unit visit prior to the interview, not only will you miss a lot of potential learning from looking and listening, but they won't think you're serious about the role.
Might also be worth visiting the centre and also getting a tower visit. You're lucky being so close to both types of unit, and will have "one up" on the other candidates. Not always possible to visit both disciplines if you're stuck on any of the county's extremities!
If it's the tests, then it's nothing to worry about. All you need to do is read the supplied information, practice any of the psychometric tests you can do online (such as the fast-track civil service one) to give you a flavour of what they're like, re-learn your 6 times, 4 times, 3 times tables and above all, revise like hell!
Best of luck, all in all it's a fun process.
WF
