The Inspiron m101z's with the dual-core Athlon II chips usually retail for £425 to £499 on Dell's site. Please note, the price posted is approximate, it'll depend on the deal you get, the £230 figure given is somewhere in the middle.
This model has been highly rated on review sites such as TR: http://www.trustedreviews.com/laptops/review/2010/08/19/Dell-Inspiron-M101z/p1
Today I got the top model (usually £499) for just under £260 with voucher: 2BDMDNDQDVHX2Q
There are several still there. Delivery is just under £20. Don't forget to use the voucher to bring down the price further!
Specs note: The difference between the two dual-core models are the cheaper one has 2GB of DDR3 with 250GB 5400rpm HDD, whereas the expensive one has 4GB DDR3 with 320GB 7200rpm HDD. The K325 processor's approximate equivalent speed-wise is the Intel ULV Pentium dual-core 1.4Ghz as seen in the review link above. As an added extra, this comes with an AMD southbridge which include graphics faster than the x4500mhd usually found in Intel C2D notebooks of this size.