It can be done but only on a very small scale because the water flows from these rivers are too sluggish.
However there are three or four locations where very large hydro-electricity plants may be technically feasible because of the large quantities of rapidly flowing water.
The Severn Estuary is one possibility but the capital cost of building such a barrage, and the accompanying 300 turbines, would be £20b.
Large-scale tidal hyrdro-electricity plants are a possibility for the distant future but a lot of development work is needed before we will know if it is a sensible proposition.
And there are many environmental campaigners who will protest about the impact of tidal power plants on wildlife.
For example, millions of birds feed on the Severn's tidal mud flats and a Severn Barrage would be illegal under the European Union's habitat directive.
Tidal power clearly has major difficulties to overcome and that is why the Government has at last decided to encourage the construction of modern, low-waste nuclear power stations.
The decision has come very late because they allowed themselves to be intimidated by the relentless protest campaigns.
The new stations will therefore not come on stream until 2020 or later and, to bridge the "energy gap", the Government wants eight huge "CO2 emitting" coal-fired stations to come on stream over the next few years.
So Britain's CO2 emissions will actually increase because the anti-nuclear campaigners have delayed the building of the much-needed new nuclear stations.
Another example of the law of unintended consequences in action.

Jim Allan,
Hartlepool.