Dont mess around trying to clean up old and tatty trim on your mini or any other car, invest in some wire wool and a few cans of satin black spray paint. Especially on black plastic scuffed trims along sills on doors even bumpers etc. Takes a few minutes to rub over and spray and cheaper paints clean off easily with thinners or polish. Not forgetting that thinners will go through paint so work fast.
Most upholstery, viynl and plastic trim inc the roof lining can be cleaned with mr muscle the original one in the yellow spray bottle. It will mark paintwork but aggitated with a small washing up brush will work wonders.
Dead insects on your chrome grill and or windscreen will be easily removed by using a very fine wire wool first before a proper clean. Used in a large ball it will not scratch either. Be careful though i have been using it for years and never had a problem.
For a perfect looking set of tyres ( if thats your thing) use shoe polish and a shoe brush. They look clean black and like tyres should look. The stuff you buy makes them look like they are coated in gloss black paint, Yuk! Also it just wipes off the wheels should you touch them.
As a last tip when cleaning your car esp minis take time to take off bits of trim once in a while and grease the backs ie light rims, hub caps,most chrome bits and bobs as we all know this is where the water loves to sit.
Silly ideas you may think but my clubman is mint, very mint for these very reasons