Pie Man, the problem with the radar is that there are holes in the bottom of the lobe at those ranges. Waddington and Scampton probably can see below 4000ft but the problem is that this can not be guaranteed. The main problem is with non squawking traffic climbing out of the numerous small airstrips around DSA especially Sandtoft as it is some 10nm further north. This traffic pops up as the B737 is turning onto the ILS, a particularly vulnerable phase of flight.