I don't know of an exact equivalent, but in that circuit I think they chose the irf530 mainly because it is very cheap and has a low on resistance.
If you are going to buy from a Maplin shop, then they sell an irf730 for 99p or an irf830 for 74p which I think should work ok in that application.
If you are buying online, then rapid electronics (
www.rapidonline.com) have the IRF530NPBF or irf510 very cheap (although delivery starts at £3.45 +vat unless you spend £25)