The extensions are aligned with the runway for instrument approaches.
The following is an excerpt from the Aeronautical Information Manual (AIM,
Chap 3. Airspace, Section 2. Controlled Airspace)
e. Functions of Class E Airspace. Class E
airspace may be designated for the following
Surface area designated for an airport
where a ...
Since you want something beyond "My mate told me...", look no further than the UK AIP ENR 1.1:
5.3.3 Gas Venting Operations
184.108.40.206 Severe turbulence and power fluctuations in turbine engines could be experienced over gas venting sites during venting of natural (methane) gas under high pressure. Locations of gas venting sites are listed at ENR 5.3.
Gas venting stations sometimes release natural gas at extremely high pressures, so there is a risk of strong updrafts or turbulence. In any case if you fly directly over you may be going through a cloud of combustable gas which could possible ignite. It's a low risk, but given it's rarely a problem going around them it would be my advice to do so.
The Kármán line is considered to be the upper limit of airspace and the lower limit of outer space. According to the Outer Space Treaty of 1967 outer space cannot be appropriated by nations (nations cannot claim ownership of parts of outer space).
In that sense, one would be able to fully legally avoid navigation (and other) fees and bureaucracy imposed by ...