The cross-party Science and Technology Committee has accused ministers of letting moves to create a network of areas that protect the UK's seas and their wildlife "flounder".
Some 31 marine conservation zones (MCZs) – covering an area around three times the size of Cornwall – have been proposed.
But the figure only represents a small proportion of the 127 "underwater national parks" that were recommended by independent advisors.
Off the South West coast, just 15 zones were signed off from 58 previously earmarked. The zones, Labour's flagship environmental legislation in government, will protect dolphins, basking sharks and pink sea fans off the Westcountry coast. But the fishing and shipping industries fear restrictions will put livelihoods at risk. Padstow Bay, the Tamar Estuary and Tor Bay are expected to be among the first wave.
The committee said the Government appears to have increased the amount of scientific evidence needed to support the designation of the protected areas, which chairman Andrew Miller MP said amounted to "shifting the goalposts".
It has been more than three years since the Marine and Coastal Access Act was passed to pave the way for the creation of MCZs, but as a result of delays in the designation process, sensitive environments have been further degraded and industries such as fishing have been subject to further uncertainty, its report said.
Cornwall MP Sarah Newton, who serves on the committee, said the report also flagged up concerns over the loss of fishing or leisure activities should be taken into account when designating the zones.
The Conservative MP for Truro and Falmouth MP added the report detailed how just one-fifth of the UK's coastal waters have been mapped – underlining the need to ensure the scientific evidence was robust.
A proposed zone around the Fal Estuary, which critics warn will threaten "350 years of history and shipping power", is among those to miss out.
Mrs Newton said: "This is a very ambitious thing the Government is trying to do. And if you are finding the right balance between protecting the environment and the economic impact, you have to make sure you have the best available evidence. This will impact communities, potentially very significantly."
But former Environment Minister Ben Bradshaw, Labour MP for Exeter, said future generations "will not forgive us" if the reserves did not come to fruition. He said: "The threat facing our seas is the biggest environmental challenge after climate change."
