On Sunday 15 April at 16.01 British Summertime (15.01 GMT) the British Geological Survey recorded an Earthquake measuring 0.7 on the Richter Scale occurring at a depth of 7 km beneath the Cumbrian village of Ambleside, at the north end of Lake Windermere. It is highly unlikely that such a small event have been felt by anyone, and it is doubtful that they would have recognized it as a quake if they did. This was followed 101 seconds later by a second quake in more-or-less the same location and depth that measured 2.0 on the Richter Scale. This second quake is far more likely to have been felt, though it was still small enough that any damage or injuries would be highly unlikely.
The location of the 15 April quakes.
Cumbria is probably England's most Earthquake-prone county, although this is hardly a major achievement in a country where major quakes are extremely rare (twelve years into the twenty-first century Earthquakes have caused a single injury in the UK, in Lincolnshire in 2008). Most quakes in northern England (and slightly more quake prone Scotland) are attributed to glacial rebound; during the most recent glaciation (the Devensian) Cumbria was buried beneath up to 900 m of ice, which did not clear till about 14 000 years ago. This much ice weighed down heavily on the rocks of Cumbria (as well as scouring the landscape and carving out the lakes of the Lake District), and they are still rebounding from the load.
The UK is also effected by movements on tectonic plate margins, even though it is a long way from any of these. The Atlantic Ocean is spreading at a rate of 20-40 mm per year, pushing Eurasia eastwards and North America to the west. Africa is pushing into Eurasia from the south at slightly over 20 mm a year; this causes regular quakes in southern and southeastern Europe, but the northwest of the continent is not immune. In addition there is some spreading occurring in the North Sea, the Rhine Valley, and the Bay of Biscay, of of which place pressure on rock formations in Britain, which can contribute to quakes (realistically most quakes are causes by a combination of all these stresses).
If you felt the quake you can report it to the British Geological Survey here. The BGS is also interested in hearing from people in the area who didn't feel the quake, which is also useful data.
See also Earthquake in Yorkshire, An Earthquake off the coast of Margate, 8 April 2012, Southwest Poland hit by Earthquake, Zurich shaken by mild Earthquake and Earthquakes on Sciency Thoughts YouTube.
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