The problem with trying to get LL inbounds in trail is all to do with the size of the UK. For example coming from the east (northern europe, eastern europe, far east, middle east and scandinavia) you have about 60 miles in which to stream the traffic and you very regularly get 6-8 at a time and another 4 very close behind, you can't get 10 miles in trail let alone 20. To do that MAAS would have to start streaming for us over northern europe and to be frank they are far to busy with their own problems to do that.
1985, I salute you from MAAS (via COA & DENUT) and lift my hat gracefully for your understanding of our situation. As you rightfully say we do have our own problems (the Belgian UIR with up to 2300 flights per 24h is as full as an egg) but whenever we can we will try (on demand or on own initiative) to provide longitudinal (preferred) or lateral separation. Despite ourselves being busy I never cease to be amazed at the amount of traffic we are throwing at you guys down the line and how you are handling it.