Seeing that you are a professional UK taxi driver then I would look it one of these GPS units.
The reason I say this it would be a tax right off for your work as a taxi drive.

See link below:

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There are many models to pick from that would meet your needs.

TomTom NDS is OK, but it has not been updated for a long time.
You still get maps for it.

Now if you want to have it work with Android Auto there are many GPS apps on the market that do a great job.

I take a taxi many times a year and what I see the drive using has always been Google Maps.

But that is up to you as to what will fit your needs.

I hope this helped you out.....