I passed through J25 on the A12 yesterday and I counted at least 3, possibly. 4 Alpha 6s . Sadly, I came through during the day so obviously can't say if they still work or not It's better than you think - there's actually 7 Alpha Sixes at junction 25 of the A12, and they are all still working!
There's one on the Marks Tey roundabout to the west of the A12, one on Station Road just off this roundabout (column 1), one on the Prince of Wales roundabout to the east of the A12, one on the dual carriageway between the two roundabouts and three on the southbound on-slip from this roundabout (columns 3, 10 and 13). These are old photos, but they're worth sharing again!
The Alpha Six on Station Road, as photographed in March 2012. If my memory serves me correctly, it has been re-celled for part-night lighting as it falls under Essex County Council's jurisdiction.
The Alpha Six on the dual carriageway linking the two roundabouts, also photographed in March 2012. The Alpha Six is on the first column on the left hand side. This Alpha Six and both the Alpha Sixes on both roundabouts have not been re-celled for part-night lighting as they fall under the jurisdiction of the Highways Agency.
Two of the three Alpha Sixes on the southbound slip road onto the A12, also photographed in March 2012. Although only columns 10 and 13 feature in this photograph, all three Alpha Sixes on this slip road have been re-celled for part-night lighting.
Colchester also has six more Alpha Sixes in nightly operation, bringing the total number of Alpha Sixes in the town to 13, which is pretty amazing considering we are in 2014.
There's one on the northbound on-slip onto the A12 at junction 26 which you may have also spotted yesterday. This is Highways Agency property so it has not been re-celled for part-night lighting.
Heading north from junction 26 on the A1124 Halstead Road and just off of the junction, there are two more Alpha Sixes:
This one, photographed in May 2013, which has been re-celled for part-night lighting.
It used to be one of a cluster of three Alpha Sixes that were originally here, suggesting that the whole road once used to be lit by Alpha Sixes:
The same location photographed with three Alpha Sixes in 2008.
And here's the other Alpha Six just north of junction 26 of the A12:
The second Alpha Six on the A1124 Halstead Road, photographed in May 2013.
The three other remaining Alpha Sixes in Colchester are on the Spring Lane roundabout just off of junction 27 of the A12, and all have been re-celled for part-night lighting. One is on the traffic island as you head towards Colchester town centre from this roundabout, another is on Spring Lane (column 2) just off this roundabout, and this one pictured below is on the roundabout itself:
The last remaining Alpha Six on Colchester's Spring Lane roundabout, photographed in April 2013.
I believe Colchester is the last location in the UK to still be running Alpha Sixes in nightly services, but I'd be happy to be proven wrong!