The study, which cost £896,681, concluded a fixed link across the Irish Sea could cost as much as £355bn and would be “impossible to justify”.
Mr Smyth said: “The news that the study into Boris Johnston’s bonkers bridge or tunnel cost almost £900,000 is completely shocking and a total disgrace.
“It is an example of yet more empty rhetoric from the UK Government and what is worse is that they spent this money on a feasibility study into building a structure which no-one truly believed could be built.
“Presumably someone finally realised that we don’t have a Mediterranean climate in the Irish Sea and any bridge would have been closed for half of the year, not to mention the small issue of millions of tonnes of explosives lying in the path of any structure in a deep channel.
“If the UK Government has billions of pounds to spend on transport links in the south west , it would do better to spend the cash on reopening the Dumfries to Stranraer rail line and dualling the A75 and A77.
“Despite the importance of Cairnryan Ferry Port, road and rail links have been neglected again and again.
"Talk of building a bridge or a tunnel might grab headlines, but people who live in the area need real solutions to the many transport problems.”