Funding ran out, can I leave
Unless UK universities differ significantly between each other, your supervisor will not have any role in assessing your final thesis - this will be done by the internal and external examiner.

Your supervisor will normally propose these based on personal experience - and I suspect in most cases the university will go along with those suggestions (at least that was my experience).
So a malicious supervisor can give you an examiner who will give you a hard time - while a friendly supervisor will suggest a friendly examiner.

So where am I going:
If the relationship with your supervisor has deteriorated to the level where you feel you would just quit - but are nevertheless motivated to complete your work, it would be highly advisable to seek some advice within the university (and possibly also if you aren't motivated to make sure you don't make a mistake). There should be a person responsible for dealing with such situations - I forgot what they are called...
Ideally, you could be given an administrative supervisor and submit the thesis under their "guidance" - they won't need to be an expert in the field, but should understand your work.

The key question in this case is whether the work is sufficient to be considered for a PhD, but only you or your supervisor (be it old or new) can determine that.

A side note on funding:
The university as an institution is unlikely to continue your funding, unless you are employed doing some work, say on a part time basis to carry on with your work. Where people are paid beyond the standard grant duration, this is done by the department - potentially the sponsor if there is an industry sponsor. I believe it is up to the department ow they organise this - i.e. whether they pay you to write up or whether they pay you to continue/complete your work before/after writing up but before defending the thesis.