There's no 'daylight saving time' in Dubai, so they're 4 hours ahead of the UK in the winter (when GMT applies here) but only 3 hours ahead during the summer (when BST is in operation).
Emirates quote 7 hours from LGW to DXB. (Some flights are shown slightly shorter, as 6 hour 50 minutes). The return flight (against the prevailing winds) is shown as 7 hours 25 minutes.
I recall a pilot or first officer on a flight to Saudi getting suspended for saying "Ladies and Gentlemen we are approaching Saudi Ararbian arirspace. Please retard your watches 2000 years" Rotfl