There's a seller on ebay that has K&N 153 oil filters for sale at £7.41 delivered, which is quite a saving on the usual £10 + delivery price at most retailers!
http://www.ebay.co.uk/sch/i.html?_fr...6n+153&_sop=15 These filters are ideal for use on DD bikes as they have a pre-drilled nut on the end, making lock-wiring your oil filter very easy!
HTH!