how can I get gmt offset value for my current time

[LONNV]

I try to calculate London market time

in my market watch server time is 20:58 PM (9:58PM)

in https://greenwichmeantime.com/ GMT is 7:43 PM DST UK is 8:43

market watch server time is ahead of 2 hr (GMT) 1 hr(DST UK) nearly

if I calculate for current time

    int CurrentHour=Hour(); // Server time in hours
    double CurrentMinute =Minute(); // Server time in minutes 
    double CurrentTime=CurrentHour + CurrentMinute/100; // Current time

it get value is same as market watch time(server time)

So I need to add gmtoffset manually or auto ,

if auto ,use TimeGMTOffset();

if manual, add 2 or 1 (gmtoffset )

double CurrentTime1 = CurrentTime + gmtoffset;

what is correct way to get UK market open time

if (TradeEuropeanMarket==true)
{
if(7:00 < 12:00){
if(CurrentTime1 >= 7:00 && CurrentTime1 <= 12:00)
TradingTime=1;}

if(7:00 > 12:00 ){
if(CurrentTime1 >= 7:00 || CurrentTime1 <= 12:00)
TradingTime=1;}
}

mainly depend on CurrentTime1 value , it depend on gmt offset.

what gmtoffset value should use.