More slow progress!
Frustratingly slow progress due to life and terrible whether continuing to hamper me. My garage is currently full of other half finished projects at the minute waiting for paint when it gets warmer, so I'm stuck working outside for now.
Anyway, let's have a talk about number plates first. (Then we can get on to the foot rest.

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(This is my solution, there are of course others, but none are perfect as that front plinth is just a carbuncle!)
So we're stuck with the Chinese format mountings for number plates on the 5. This means four holes at the rear in the wrong place to suit our standard plates and that great big, incorrectly sized plinth, moulded into the front bumper. They even added two sizeable holes in it, just to ensure maximum difficultly when trying to make a standard UK plate fit and look anything like reasonable. (Which you just can't!)
So the answer is to make plates that are closer to the Chinese plate standard.
The ideal depth is 140mm, this fits the front plinth perfectly as well as allowing the use of all four bolt holes to the rear, if mounting this way, or covering them adequately if mounting with self adhesive pads.
As for width, the standard UK 520mm length leaves the front plate sides flapping about way over each end of the plinth and looks terrible. At the rear, when using a 140mm depth, it will also hit the badging if you're keeping it, unless you were to fit off centre. So we need the plates to be shorter. The good news is UK plates don't have to be 520mm, they can be shortened to 457mm whilst accommodating our 7 full sized digits and legal borders. This fits the front plinth really nicely with only a slight overhang to the sides and clears the rear badging. (If you're keeping it)
So 457mm x 140mm it is, let's get some ordered. Well... no... Because nobody will make you this size. Some providers will make you a 520mm x 140mm, and some will make you a 457mm x 111mm, but no one will make a 457mm x 140mm!
So here is my own answer to that one. I bought 520mm x 140mm plates from Proplates, to include the UK identifier to the left and what they call an internal border.
So this is what you get:
Obviously not actually that, there's a couple more letters, but internet and security, you know how it is.
And after a quick session with this little lot:
20 minutes later, we have both front and rear plates looking more like this:
Because I've gone with the border, the end result is actually 470mm wide in my case, which I'm just fine with as I like borders.
And here's the front plate fitted:
I've used adhesive pads for the smooth look, as I don't personally like bolts much. A tip for when you're using pads. Clean both the rear of the plate and the plinth with alcohol. (The medical stuff, not Vodka or Gin!) Only fit when it's totally dry, never in damp conditions, and warm both the rear of the plate and plinth thoroughly with a hot air gun until the surfaces are nice and warm. This will guarantee perfect adhesion every time.
So, the plate is now the right depth, matching the plinth, with an overhang of only 25mm each side. Much better. I still don't like it much, but it makes the most of a bad job with that big, ugly, plinth and now doesn't look like a total Heath Robinson!
Finally for comparison. Standard plate vs 570mm x 140mm.
I can't show you the rear plate yet, as when getting ready to fit it, I noticed a nasty flaw in one of the letters, so it's getting replaced. I'll edit this and add a rear pic in due course.