The ATM journal Mathematics Teaching has a very nice (and growing) archive where several back issues are available in PDF format. Some articles/issues are only available to ATM members, while others (quite a few, actually!) are available to all, for free. In the archive, you can even take a closer look at the first issue (ever) of the journal, from 1955.

So, if you are interested in mathematics teaching in general (and in the UK in particular), you should definitely take a look! Hopefully, the archive will continue growing, and I wish other journals would follow up and do the same thing (preferably with a large collection of freely available back issues)!