MR100 UK Disconnection problem

[FilB]

Three days ago my Nighthawk began to disconnect itself from the network.
Every 30 seconds or less it disconnects then reconnects. It's doing this repeadly making the device unusable.
We rely on this router for all our internet and boat alarm system as we travel the Mediterranean on a sail yacht.
The network provider is Vodaphone in the UK

It disconnects so quickly it's not up long enough to access the settings in the router before it closes down again.
I've seen similar posts mostly from US users but the solutions here don't seem work.
We're desperate to get this running again as its provides our weather reports and ultimately our safety.