I think I will be able to solve your wifi signal issue remotely. If I can't I'm happy to fly into Stanstead, hire a car, and drive up and fix it. I'm in Scotland, but close to Edinburgh Airport, so flying down and back in the same day shouldn't be an issue.
As such, I'll breakdown the bid into achievable milestones.
£200 initial assessment and attempt to solve the problem remotely (for this I will need you to be on the phone with me while also giving me remote access (via TeamViewer) to a computer which is connected to your network). In order to identify the problem, what I'll do is start at the router with a ping test (this can be done remotely). If the problem is there, then the problem may be with your line, and not with your equipment.
If a ping test and connection strength analysis come back reporting no problems, I'll reconfigure your router settings, and start trouble shooting your connection.
If I can't solve the problem remotely, which may take a few sessions with yourself as you may need to purchase a new extender, I'll fly down to you to fix it.
Which brings me to the second milestone.
£450 for an in person visit.
This will cover a return flight from Edinburgh to Stanstead, car hire for the day, and my time.
If I can fix it remotely (which I think likely), we can cancel the second milestone.