A CFML function to determine whether a date is in GMT or BST for the Europe/London region

getDateTimeZone.cfm

	<cffunction name="getDateTimeZone" returntype="string" access="public">
		<cfargument name="the_date" type="date" required="true"> 

		<cfset var local = {}>

		<cftry>
			<cfset local.timezone = "">
			<cfset local.obj_timezone = createObject("java", "java.util.TimeZone").getTimeZone("Europe/London")>

			<cfset local.is_daylight_time = local.obj_timezone.inDaylightTime(arguments.the_date)>

			<cfif local.is_daylight_time>
				<cfset local.timezone = "BST">
			<cfelse>
				<cfset local.timezone = "GMT">
			</cfif>

			<cfcatch type="any">
				<cfset local.timezone = "">
			</cfcatch>
		</cftry>

		<cfreturn local.timezone>
	</cffunction>