So we have
1) Chopsticks at the A21/A224 roundabout with "M25" (ditto at Sevenoaks J6)
2) Signs on M25 indicate it to be A21(M) due to signing it as A21 not (A21)
3) Whatever it is, it is the (A21) as the old A21 is A224 and the M25 immediately becomes the A21 at the chopsticks at Sevenoaks.
4) The roundabout A21/A224 does NOT have a junction number (ie the equivalent roundabouts on the Luton airport spur /Gatwick Airport spur on the M1/M23 are numbered as part of those motorways ie 10A 9A
5) Maps show it as M25
6)
At junction 6 the main line of the Road is signposted as "Sevenoaks, Hastings A21" despite the fact that it is on an even longer spur1) Can be dismissed as exactly the same occurs on several other sites to avoid confusion (eg the now gone and unlamented M15 was signed as Junction 3 of the M11 with M11 chopsticks to avboid confusion)
5) So can (5) as maps are not reliable in this (try finding A14(M) on a map)
The balance of probability tilts towards A21(M) at both ends as given that the motorway is M25(A21) between J5 and 6 if the spurs are M25 they should most certainly be signed as (A21) but that is not really enough proof
So lets head south from that last google link...
Hmm this looks interesting.Note the slip road states states
M25 Gatwick (M23) Heathrow (M4)
Therefore the main line of the road should state
M25 Sevenoaks (A21) Hastings (A21)
But it actually states (in Blue)
A21 Sevenoaks Hastings
Even more interesting, this spur is over a mile long and has its own junction. If it is part of the M25 why does that junction not have a number, and why is there only "A25" for the slip road and no number for the main line at all on that sign?
A bit further on
thats a bit better and would be consistent with the motorway being M25 so perhaps it is M25 after all?
But wait
take a closer look
* That sign says for the main line "Hastings A21" in green
* but it says for the first slip, which is before the end of the Motorway "Sevenoaks Riverhead A25" in a white box on a blue background.
If this stretch of road was the M25 then
this sign would state
M25 Sevenoaks (A2
5) Hastings (A21)
It does not, it states
A21 Sevenoaks Hastings
And here is confirmation that you turn off for sevenoaks onto the A25 prior to the end of Motorway regulations (just)And of course when that stretch of road opened it WAS the A21 as it was built before the M25. It was part of the A21 Sevenoaks Bypass and was placed under motorway regulations some years later when the M25 was built, hence the substandard hard shoulders.
Therefore that stretch of road can only be the A21(M)
I declare a secret motorway
Bravo. I'm not convinced by the J4 spur being the A21(M), but by god junction 5 should be. It is signposted as the A21, has its own Motorways merge signs sounthbound, Southbound is the mainline and has its own GSJ junction. Easily up their with the A14(M). Extend it to Tonbridge I say while we are on the subject, its such a good piece of road.