Before official distribution in the UK of original Superman comic from American in November 1959, one way to get your Superman fix was through Australian reprints which were then made available in the UK, cover priced 6d (Australian issues were cover priced 8d/9d. They tend to be newsprint quality covers while the UK editions tend to have glossy covers).
It's very confusing when you see two copies of Superman with the same number but different covers and cover prices (see Superman All Color Comics). The answer is of course that one is an Australian reprint (the 8d/9d ones) and one is the Australian reprint for the UK market or UK variant copy (cover priced 6d). They tend to be a couple of years apart in publication date with the Australian 8d/9d one published first. Values about the same.
Note: a very interesting pre-publication no-number copy of Superman #1 was sold by Comic Book Postal Auctions for £253 in their Spring 2008 catalogue. It is thought that there are only two existing copies. (NB Oct 2014. I have seen a third copy!) It was a reprint of the Australian edition #1 from June 1947. It was very much a market-tester issue by the publishers in the UK who were no doubt deciding whether or not to publish Australian editions of Superman in the UK. Once again another amazing item of historical importance found and marketed by one of the UK's great comic authorities Mr. Malcolm Phillips. Nice one Malcolm.
Honorary mentions too for ausreprints.com and bookpalace.com for their pioneering work in collating covers for this series.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.