Hmm... Tricky...
I've not had to deal with imperial gas meters before, so I had my friend Blastoise186 gave me some advice over the last couple of days. I think I can figure this out from here.
As far as I can tell, that meter seems to be spinning a little faster than I'd like, but I'm not quite sure if it'd be fast enough to justify an OFMAT. I'm kinda borderline though so it's hard to say for sure - it could just be that your heating and hot water system is really inefficient! However, with that being said... We are talking about a 29 year old gas meter here and they are known to get a little out of sync as they get older.
Personally, I think what I'm about to say is probably the best advice I can give for your situation, so I'll explain what I think. For anyone else reading this, please be advised that the same circumstances may not apply to you and you should also perform a Burns Test for yourself before going any further, if you think you have a faulty gas meter.
I definitely think it's time for a Meter Exchange regardless of faults and there's no escaping the fact it's an ancient meter which is overdue for recertification anyway. I feel that's definitely something anyone would agree with me on. I'll let you decide whether you're ready to do that, so feel free to take it at your own pace. Going for Smart Meters might benefit you, but again, I'll leave that up to your discretion.
As for that OFMAT? Hmm... This is a really, really tough call for me to make and I'll totally understand if you decide to do the opposite as it really is borderline. At this stage, the worst that could happen is that you basically end up "buying" a new gas meter for £160 if the current meter passes the OFMAT, if you get what I mean. However, if the current meter fails the OFMAT you'd not only get the meter replaced anyway (gas meters are ALWAYS replaced during an OFMAT) and your £160 back, but you may also get a refund for any overcharges.
Based on the information you've provided, the stuff that Blastoise told me and the age of the meter, I'm going to recommend taking up the OFMAT process and getting the gas meter tested. It would have to be replaced sooner or later anyway and this would have the additional benefit of you knowing whether you've got a horrible gas meter, or a horrible boiler. :)
I hope this helps. Please let me know how you get on.