You have no right to see the will before probate is granted (although there is absolutely nothing to stop your aunt showing it to you if she wants to).
Executors are placed in a position of trust to ensure that the terms of the will are faithfully carried out. If they fail to do so they can be held personally liable for any losses suffered by a beneficiary. (If the executor fails to ensure that a beneficiary receives their share of the estate, that beneficiary can then sue the executor, forcing them to pay out of their own pocket).
All wills become public documents once probate has been granted. Anyone who anticipates that they might need to contest a will (or, indeed, anyone else who is interested in it) can enter a standing search with the probate registry. (There's a £5 fee for the service, which must be renewed after 6 months if probate hasn't been granted within that period). As soon as the grant of probate is issued, the person who has entered the search will receive a copy of it (which includes a copy of the will):
http://www.hmcourts-s...e.gov.uk/cms/1211.htm
Chris