What to do before you call
Water, gas, power and a locked door. You call the firm yourself.
Water
Shut the main stopcock. If you do not know which valve that is, shut the valve under the leaking fixture. Switch off power to the wet area. Then call. A card on the plumbers list is a firm you call yourself.
Gas
Leave the flat. Do not use switches, doorbells or a phone until you are outside. Call 112 from outside. This page does not send anyone.
Power
If one circuit has tripped, leave it off. Do not open the distribution board. If you smell burning, leave and call 112. For a single dead circuit in office hours, use the electricians list.
A lock
Do not force the frame. Call a firm from the locksmiths list and agree the total, trip included, before they start. A card marked 24h is the one that has offered round-the-clock cover.
Cold heating, no leak
A radiator that stays cold, with no water coming out, can wait for a daytime appointment. Say that in the first sentence so the firm does not treat it as a burst pipe. If water is actually running, go back to the water steps.