Take a tripod? (If you can/are allowed to) Long exposures/bracketing could allow for something special...
Shoot a series of photos at different exposures by setting your dSLR's bracketing system. The camera takes the first picture at the metered exposure, and then it takes the second and third at, say, one-third stop less exposure and one-third stop more exposure. You can set the exact increment, choosing to bracket by half or full stops if you want. You can also bracket parameters other than exposure, such as white balance and flash. Your camera might allow you to bracket more than one of these, and in the order you choose.
Can you take a tripod with you? Long exposures will be much better because I am presuming its going to rather dark inside.
I say most cathedrals are ok with photos, but you may want to ring ahead and ask to avoid any nasty surprises...
If anyone does visit the cathedral then you need to go to the gift shop and purchase a photography pass (£2) they seem quite strict about this as I was checked a few times ....... I don’t blame them though and £2 is a bargain for a fantastic place.