Motorway Gantry Speed Limits

BlackLion79

I was recently driving on the M1 and noticed that the gantry signs were showing different speed limits across the lanes (e.g. left lane had 60 limit, whilst middle and right lane were showing national speed limit). Also, this wasn't even consistent between consecutive gantries (so different lanes showing 60 and national speed limit from one sign to the next). 
This happened for several miles and gantry signs, before all lanes started showing the same limit. I assume there was an error in the system and played it safe by sticking to the lower speed limit (60mph) regardless of the sign above my lane. However, I was wondering about the legalities - can a driver be prosecuted for speeding if the lanes show different limits?
Incidentally, I remember being told in a Motorway Awareness course that the gantry signs should always show the same speed across motorway lanes, but I guess they weren't accounting for system errors!

ontheroad1970

Did they have red circles around them?

BlackLion79

ontheroad1970 said:

Did they have red circles around them?

Yes, lanes with 60 limit had number in red circles. Other lanes had the national speed limit sign.

spiro

BlackLion79 said:

Incidentally, I remember being told in a Motorway Awareness course that the gantry signs should always show the same speed across motorway lanes, but I guess they weren't accounting for system errors!

I you travel round the section of the M25 near Heathrow where it is about 5/6 lanes wide it is common for the left hand lanes to have a lower speed limit than the other lanes. This is not a fault but because the traffic in the lefy lanes are approaching a junction where queues are common.