Shuka,
What you need to do is have a professional snagging inspection completed (if you can afford it great, if not there are
checklists you can download and print out on this site).
A professional will take a fair few hours to inspect and should email you a completed, full report. If you are doing this yourself then you should be taking hours as well. You should have it professionally done if you can.
Then once you have the report, email it to their sales team and the site manager and state this is what you have picked up (so far) and everything needs to be rectified before you legally complete on the property or you will not do so. Do this via an email, in the same email cc your solicitor and state that they are not to complete until they have received written authority from you to do so. I would do this so everyone knows where you stand and the fact you are serious about it!
You also have two years in which the house builder is responsible for rectifying snags but you are absolutely right to get them done prior to handover of your house. You should have received a booklet staying your aftercare service and your right to go the resolution service of you are not happy how they have dealt with your issues.
Barratt are usually one of the better ones, see how your meeting goes but I would confirm everything in an email for evidence from outcome of the meeting.
Don't let them fob you if with stuff like within tolerance, if it's not right it's not right. Be strong don't settle for anything you are not happy with.
Please list outstanding faults, this will aid specific advise to you.
Good luck