length of a phd thesis

When you submit, you will be asked to certify that your thesis falls within the relevant word limit.
In exceptional circumstances, the Dean—Wellington Faculty of Graduate Research may grant permission for you to submit a longer thesis. You will need to apply for permission to exceed the word limit well in advance of submission.

The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336, VAT Registration Number GB 592 9507 00, and is acknowledged by the UK authorities as a “Recognised body” which has been granted degree awarding powers.
The Postgraduate Degree Regulations stipulate the word count for research degrees.

References:

http://www.ed.ac.uk/history-classics-archaeology/current-postgraduates/phd-students/thesis-viva/thesis-length
http://www.monash.edu/rlo/graduate-research-writing/write-the-thesis/writing-the-thesis-chapters