The routes to and from major airports are all available in the public domain. Go to this link, register and then look up what you need in the AIP. None of the maps are of OS-style though:
http://www.ais.org.uk/aes/login.jsp;...422922!80!7002
You should be aware of the following:
Departure routes are fairly standardised, ie aircraft will usually follow them except when the weather is very bad. Arrival routes are fairly standard until the aircraft reach the holding areas associated with the airfield in question. Thereafter the "routes" to the airfield will vary at the discretion of the radar controllers.
That said, radar control is employed in most of the major hubs in the UK so routes may vary slightly depending on traffic situation.