In time many taps become very difficult to turn, this is because most water in our country is hard in nature meaning that it has lime in it, the reason the taps become difficult or in some cases you find the not much water comes out is because it has become scaled up. Fixing the problem is not really difficult for a reasonably capable DIY person.
Turn off the water at the stop cock, you may have individual isolation valves on the pipe leading to the tap, if it is the hot water tap you will have to drain off the system by turning off the feed to the tank in the loft. Turn on the tap to make sure no water comes out.
Remove the valve by taking off the handle or knob which will be usually held on by a screw under the hot or cold symbol on the top. Using an adjustable spanner turn the vale anti clockwise this will also reveal a standard type of rubber washer which should be replaced at the same time; it could be a disc which will not need any attention.
Inspect the valve and it will probably have a lot of lime scale which can be removed with lime scale remover and finally grease it with silicon grease, normally available at you plumbers merchant. If the scale will not easy come off it may be best to just change the valve by buying a new on at the plumbers merchant. A word of caution, take the valve with you so it is perfectly matched, they are not all the same. A new one should not cost a lot more than about £5.
Picture: Dan Harvey