Flights from London (not just Gatwick) to Venice will often fly over Kent, England, then across the English Channel and along the border of northern France and Belgium (passing over Luxembourg), then the plane will turn south over eastern France, south central Germany, western Austria and then over northern Italy before descent into Venice.
A flight from London to Greece will firstly fly East over Kent and the Medway towns in England, then the plane will cross the English Channel and fly over Belgium, passing directly over Brussels. Then the plane will fly over southern Germany, passing close to Frankfurt, then the flight will torn southeast crossing the Alpine region of Austria, then the flight will fly over Slovenia, Croatia, Bosnia, Montenegro and Albania before descending into Greece.
Usually northeast over the atlantic, then southwest to London, heading over Belfast.
If you look at a map you will see that Dubai is on the Persian Gulf near the Strait of Hormuz. Draw a straight line to London and you will cross Germany. So I would say that you would cross Germany because that is the most direct route.
Bristol (BRS) to Venice Marco Polo (VCE) takes just over 3 hours (about 3h10m / 3h15m)
You are most likely to fly over the Scottish mountains on a flight from London Heathrow to Aberdeen Scotland.
The flight time from London, United Kingdom to Chile is: 14 hours, 37 minutes
That will depend either on the distance or weather conditions, but I expect that the flight path passes over: Kent (England), Belgium, Germany, Austria, Italy, Croatia, then over the Mediterranean sea towards Greece then towards Saudi Arabia.
A flight from Houston, Texas to London, UK will fly northeast towards New England before leaving US airspace, then the flight will fly over the area of the Atlantic south of Greenland and Iceland, then the flight will fly over Central Ireland, passing Dublin, the Irish Sea and then the flight will fly over the North Wales coast. After flying over North Wales the flight will head southeast towards Birmingham and Oxford and then into London.
It depends whether the flight is overflying London or if it is taking off or landing at London.
The flight path follows a Northeast direction.
A flight from LA to London will fly northeast towards the northern states of the USA, then over much of northern Canada, then over Greenland then Iceland, the flight will then head southwest towards the southwest tip of Scotland, then the plane will turn south over the Lake District towards Manchester, the flight will then finally head towards Birmingham before landing in London.