A single engine class rating is valid for 2 years so check when your Certificate of Revalidation was last signed. If you have a UK CPL then you automatically have IMC Rating privileges. If you have a JAA licence then you are VFR only (min vis 3 km actually). Of course, anyone hiring you a PA28 may want you to do a chack flight if you've not been in a puddle-jumper for some time. To carry pax you need 3 t/o's and landings in the last 90 days as 'sole manipulator' of the controls.