Hi Moonstone
I did a degree in archaeology as a youngster against a lot of family opposition. I've never regretted it. However I knew even back then in the 70s that the like of me would not be able to hope for a full-tme, mortgage-paying career in it, so I did a PGCE and became a teacher.
Over the years I have had paid work as an archaeologist - in short contracts here and there. I've kept up my interest and some contacts.
The injustice today is that degrees cost so much - mine came to me free of charge. So there's some sound advice in posts here suggesting you go for a batch of experiences that will help decide if, when and how you go the rest of the way in terms of qualifications.
There is no longer a GCSE. You might look at GCSE classical civilisations which is OK but it depends on where your interests lie: mine for example are very mush in field archaeology and built environments, whereas clas. civ concentrates on greek classical texts.
There is an A-level in Archaeology which very few places offer, but most people going into archaeology at degree level don't have this. You need nowse, muscle, perseverence and an analytical approach.
A word of caution: some local societies are a bit backward and don't necessarily practice a good standard of archaeology ie they go round digging random holes. You don't want to get identified with them. Might be worth making a start with your county archaeology service and your regional museums, to get advice and look for some voluntary - maybe even paid - experience.
You can also get a summary of digs, British and foreign, in Current Archaeology. Sadly many now expect you to pay to attend, but if you view it as affordable training it's not too bad.
Go for it, enjoy it.