How about:

C142 OMB illegally spaced and with a wrong colour bolt to read CL42O MB. You put a black bolt and a space at the foot of the 1, it looks effective enough. C142 OMB is probably not readily available, though.

I like A20 CLX spaced as you suggest.

In the UK, "private" or "cherished" number plates offer a mixture of personalisation and status, it is that simple. The fewer letters and the lower the numbers, the better. Combinations that spell a word are valuable, too. Words followed by numbers is preferrable to numbers followed by words: I have no idea why! Short registrations look so much better on the car.

For instance, A1 (is it still in Earl Russell's family?) would be ultra-desireable. I would expect that to fetch 250k at least. K1 NGS recently sold for that sum. FU 2 recently sold for 100k. Geoffery Archer reputedly owned ANY 1 in the 80s: would be worth a stack. One not-very-funny TV comedian has COM 1C; a TV magician has MAG 1C.

My ideal plate would be JR 1 or JJR 1. I have seen JR 1 on a Jaguar XK8 on several occasions, must be a local car. 6 JR is on sale for 23k; JR 7 is available for 38k; JJR 48 is 4k and JJR 61 is 3.25k.

My plate S5 JJR was a mere 250 quid plus transfer fee of 80. I previously chose letters that made it appear under all except the closest examination either SS JJR or 55 JJR (vanity, vanity) but presently it is simple S5 JJR.

They are going up in value.

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190