The costly mistake was only discovered when inspectors measured the finished tunnel in the Polish capital, Warsaw, and realised the roof was so low that no trains would get under it.
Rail bosses claim the mix-up happened because workers who were laying new tracks didn't talk to the team that was building the tunnel.
"During work on the tunnel, tracks were laid down on newly-raised ground which meant the distance between the tracks and roof of the tunnel became shorter," said Polish Railways spokesman Marta Szklarek.
Wiveliscombe Representative of ARD (Association of Road Diggers) Mr Sharland commented
'I went to Poland last year to discuss how best we could delay traffic across Europe using Taunton as a template. After long talks with Hans Onmeknob I went to advise the poles how to lean on a shovel, drinking coffee whilst traffic backed up.
The cock-up is the latest in a series of public transport construction fiascoes in Poland.
A tunnel built recently to divert lorry traffic in Warsaw turned out to be too low for lorries.