Astronomically, Spring starts at the Vernal Equinox, when the Sun crosses the equatorial into the northern hemisphere - at 2124 UTC (~GMT) on 20 March.
Astronomical Summer then starts at the Summer Solstice - 1557 BST on 21 June, when the Sun is at its highest northerly latitude of 23º26’; it returns to the southern hemisphere at the Autumnal Equinox, at 0750 BST on 23 September.
In 2002, the EU stipulated that all member states should adopt ’Summer Time’ between the last Sundays in March and October - the clocks to change at 0100 UTC. So, this year BST will apply from 26 March to 29 October, even though we are no longer within the EU . .
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