Here's my take on the law about ASL's. They were only invented after I retired so this is based largely on looking it up, rather than any practical experience. It's worth remembering that for a prosecution to succeed, there are points to prove. This is about the the offence called failing to comply with traffic signs.
The CPS Guide is usually a pretty good place to look for anything like this but it refers readers to Wilkinson (the traffic law bible.)http://www.cps.gov.uk/legal/p_to_r/road ... l#P84_4838
Were I still working, I should have access to this through the WY Police Driving School but I don't have access now. It's a snip at £550 so I won't be buying a copy any time soon.http://www.sweetandmaxwell.co.uk/wilkinson/
There's a straightforward explanation of ASL's in the Traffic Signs Manual - the official guide for the people installing them
Traffic Signs Manual Chapter 5
https://www.gov.uk/government/uploads/s ... ter-05.pdf
16.21 Vehicles other than cycles must stop at the first line when signalled to do so. An advisory or mandatory cycle lane, preferably 1.5 m wide, must be provided to enable cyclists to enter the reservoir lawfully, i.e. without crossing the first stop line. ....
The offence of failing to comply with a traffic sign is prescribed by s 36 of the Road Traffic Act, 1988. It only covers traffic signs specified by regulation. (NB failing to comply with other mandatory traffic signs would be an offence under the relevant traffic regulation order. The s 36 signs are not covered by traffic regulation orders.)
Incidentally, s 36 also says that signs are assumed to be kosher (my word) unless the contrary is proved - a bit of legislative loophole plugging. http://www.legislation.gov.uk/ukpga/1988/52/section/36
The signs to which s 36 RTA 1988 applies are listed in Regulation 10 of the Traffic Signs Regulations and General Directions (2002) (TSRGD for short.)
Traffic lights are listed here
(g )the red light signal when displayed by the light signals prescribed by regulation 33 ..
.http://www.legislation.gov.uk/uksi/2002 ... on/10/made
Regulation 33 quoted in reg 10 describes traffic lights in legal terms http://www.legislation.gov.uk/uksi/2002 ... on/33/made
Regulation 36 explains what the different phases of traffic lights mean, the relevant one here being
http://www.legislation.gov.uk/uksi/2002 ... on/36/made
the red signal shall convey the prohibition that vehicular traffic shall not proceed beyond the stop line ...
"Stop line" is defined in regulation 43, with a supplementary definition for when there is an ASL in reg 43(2) That refers to diagram 1001.2http://www.legislation.gov.uk/uksi/2002 ... on/43/made
Schedule 6 has the diagrams and diagram 1001.2 is of an ASL with feeder lane (nearside and central variations are shown)http://www.legislation.gov.uk/uksi/2002 ... ule/6/made
So, an ASL without a feeder doesn't comply. If a sign (which includes a road marking) doesn't comply, it can't be an offence to disobey it. At a superficial level, it might be argued that the absence of the feeder lane rendered the entire signal unlawful but it would only mean, IMO, that it had no diagram 1001.2 ie the ASL legally didn't exist.
I think that's a thread to needle explanation of what the Met's message said about the law. I've avoided any comment about enforcement policy