Maybe I misunderstood your post. I'm not at London Info and don't really know how they work, but as a controller I would never arrange airways joining clearance for anyone who hadn't asked me to. How do I know that a) they want it and b) can comply with it? There's no point in wasting my time and the airways contoller's time coordinating it if it's not going to be used. Plenty of people change their routing and decide to remain outside when airborne and the weather is better than forecast, for example. I think it's best to assume you have to ask every time.