I suspect that the ticket office is outsourced, hence the reason for the 0845 number which may well be not answered at the theatre.
Indeed, when booking tickets online, it goes to a page on the tickets.com website. Click the text "CLICK HERE TO BOOK TICKETS ONLINE!" on the left of the
contact page and you'll see what I mean.
The
contact page on Tickets.com gives:
Tickets.com Ltd.
Elder House
570-578 Elder Gate
Milton Keynes
MK9 1LR
Tel: 01908 232 404
Fax : 01908 232 414