1. Window cleaners in the UK often wear non-descript clothes and drive unadorned vehicles. This does not mean that they are casing your block for a future break-in. It just means that they're working CLEANING WINDOWS.
2. Most plumbers, electricians, and the like will already have a key to your flat (given to them by the landlord), and, on the appointed day, will simply let themselves in in order to start doing work. If you'd prefer that they don't just come in while you're in the shower, or otherwise indisposed, then put your key in the bolt lock and lock it from the inside, so that no one may enter first before you've had a chance to put your trousers on.
3. Always offer those who are checking your boiler, smoke alarms, etc... a cup of tea for their troubles. It's the polite thing to do. And, he/she will both accept and drink it (even if you live in an area where the water needs to be strained for its heavy mineral content). :S
4. Questions regarding trash collection and recycling are to be directed to your local council. Collection may vary not only from block to block, but from house to house. If you've moved into a flat/house with no actual front space, then you're to put out sacks (recycling and compost sacks are council provided) weekly on the front pavement. Your neighbor with the front garden need only drop his trash into the bins provided him while you must drag your sacks from the back garden through the house to the front on a weekly basis. -can't wait for the rain!