I have no skills or experience - an unqualified muppet...
From this pdf... Page two...
http://www.heatweb.com/pdf/Invensys/Programmer%20Compatibility%20Chary.pdf
Drayton Lifestyle LP112 terminals
Neutral
Live
1) H/W Off
2) C/H Off
3) H/W On
4) C/H On
In this diagram...
http://www.gasheating.co.uk/Mid-Position-Valve.html
H/W off goes to the cyclinder stat and from there to the Mid Position Valve on the Grey wire
Good luck...
Peccavi
February 2010