when do they change the time in london?
Greenwich Mean Time
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 In several countries , fire safety officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke and carbon monoxide detectors , particularly in autumn , just before the heating and candle season causes an increase in home fires . Similar twice @-@ yearly tasks include reviewing and practicing fire escape and family disaster plans , inspecting vehicle lights , checking storage areas for hazardous materials , reprogramming thermostats , and seasonal vaccinations . Locations without DST can instead use the first days of spring and autumn as reminders . 

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 By synchronously resetting all clocks in a region to one hour ahead of standard time ( one hour " fast " ) , individuals who follow such a year @-@ round schedule will wake an hour earlier than they would have otherwise ; they will begin and complete daily work routines an hour earlier , and they will have available to them an extra hour of daylight after their workday activities . However , they will have one less hour of daylight at the start of each day , making the policy less practical during winter . 

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 For many years , revellers celebrating the New Year have gathered in the square despite a lack of celebrations being arranged . The lack of official events was partly because the authorities were concerned that encouraging more partygoers would cause overcrowding . Since 2003 , a firework display centred on the London Eye and South Bank of the Thames has been provided as an alternative . Since 2014 , New Year celebrations have been organised by the Greater London Authority in conjunction with the charity Unicef , who began ticketing the event to control crowd numbers . 

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 Beginning and ending dates are roughly the reverse in the southern hemisphere . For example , mainland Chile observed DST from the second Saturday in October to the second Saturday in March , with transitions at 24 : 00 local time . The time difference between the United Kingdom and mainland Chile could therefore be five hours during the Northern summer , three hours during the Southern summer and four hours a few weeks per year because of mismatch of changing dates . 

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 Current practice involves a celebrity turning the lights on in mid- to late @-@ November , and they remain lit until 6 January ( Twelfth Night ) . The festivities were postponed in 1963 due to the assassination of John F. Kennedy and in 1989 to fit Kylie Minogue 's touring commitments . In 2015 , the lights were switched on earlier , on Sunday 1 November , resulting in an unusual closure of the street to all traffic . 
