Summer time is decided as the EU level:
http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:320...
But as the UK is apparently leaving the EU, staying on BST will be possible...
[EDIT, typo: US -> UK]
But as the UK is apparently leaving the EU, staying on BST will be possible...
[EDIT, typo: US -> UK]
This document only seems to specify when the switch happens for obvious coordination reasons, in the same way DST dates are decided at the federal level in the US, but states are not required to use DST (IIRC AZ does not)
http://ec.europa.eu/transport/facts-fundings/studies/doc/201...
"European policy measures began to be introduced, leading to the present day situation, where Directive 2000/84/EC requires Member States to put their clocks forward one hour on the last Sunday of March and change them back on the last Sunday of October each year."
And 11.2 (page 10): "The cumulative effect of this succession of laws is that all Member States are now obliged to observe summertime, starting it on the last Sunday of March and ending it on the last Sunday of October."