I've had a conditional offer for a PhD that I've accepted. It is, however, conditional on meeting a certain percentage in my current masters degree.

If I don't make this condition, how likely is it that I won't be allowed to do the PhD ? I'm not talking of a major difference, probably just a few percentage points under.

Well, the conditions are set, so officially it appears if you don't meet them that the studentship could go to another student who did. If you seriously think you will be under, you had best call the Supervisor and discuss with him/her to see what leeway you have.

Sometimes thay might ask you to study some extra courses but it all depends on your supervisor.

I suggest you spend less time worrying about whether you're gonna get the grades and more time studying to make sure you definitely do! Think Positive Dan!

If u dont get the grades, don't worry. Its not the end of the world.

Have they told you what the percentage is and if this is an average mark or in every module? I know where I come from (social science) 40% is a pass, 70% is distinction BUT even if you pass (at 40%)there is an expectation that a student should get over 60% before starting a phd.