A decision on whether the Croxley Rail Link can go ahead may be several months away but the proposed extension has already found its way onto a new tube map.

The unofficial circular design, produced by London Underground map expert Dr Max Roberts, shows the extension of the Metropolitan Line to Watford Junction.

Two new stations along the route – Croxley Green and West Watford – are also pictured on the line which then links to Watford High Street before terminating at the mainline rail station.

But there is not a space on the map for the current Watford station which residents made an impassioned case to preserve during an inquiry last year.

The design, based on concentric circles, is partially inspired by the completion of the London Overground loop in December 2012.

Dr Roberts told the Going Underground blog he thought it was unlikely his design would be implemented in the near future.

He said: "With the new orbital loop surrounding Central London, some people are suggesting a mapping approach based on circles to emphasise this feature.

"There is nothing new here, and Berlin, Paris, Moscow and Madrid have all received this treatment in the past.

"Grounding a map in familiar shapes such as circles can make it easy to comprehend. However, it is also possible to push a design priority too far.

"As the old saying goes, be careful of what you might desire, in case you get it."

An inquiry into the Croxley Rail Link was held in Watford in October 2012. The inspector's finished report will be submitted to Patrick McLoughlin, Secretary of State for Transport, whose decision is expected this spring.