I just learned about a nice resource from the British Library: EthOS, which appears to be the rough equivalent of the UMI database in the states. They are in the process of digitising all the PhD theses from participating institutions so that you can download them directly (mostly as pdf’s) for free or pay for a print version. For theses not yet digitised, there is only a 10 day waiting period. In addition, those listed for the past 2 or 3 years have abstracts available.
All the major Scottish universities are full participants (Edinburgh, St. Andrew’s, Aberdeen, Glasgow) and many of the English and Welsh universities. Notable absentees are Oxbridge. Durham allows theirs to be listed but not downloaded.