It's amazing some people think it is okay to lie on your CV....presumably these are the same kind of scumbags who would make a career out of benefit scrounging as well?
What many seem to miss, a CV doesn't get you a job, it nets you an interview.
Lying with regard to grades, there are 11 different services in UK alone at bare minimum to check whether or not you are fibbing on the academic part of your CV. Some even hold a record on whether you've submitted a CV before that is inconsistent with your academic record. It only cost an employer less than £10 to run a quick one on you.
With regards to your work experience, lying on it is a pointless exercise, it is even easier to check whether it's a fib or not and even easier still is to check the circumstances in which you quit from your last job.
Now it may be the case that they discover the fib after you've been hired and they may very well not do anything about it, sometimes they may even start looking into it after they find out that you are a crap employee, the consequences could be criminal prosecution, but more often than not you would find that in years to come any job you apply to would get binned as the employer may have reported it to one of the CV checking services and even if your current CVs are legit, it would still bear a mark that you've lied on a CV previously.
End of the day, why lie and make yourself something you're not, bull**** may get you a job but it certainly won't keep you there..... it is better to not have a job than to have one that you can't do and then be sacked from it.