Tides generally run at 4-12 knots along the eastern coast in a southerly direction. I'm not sure about the Irish sea but the tides on the west coast are twice the height as those on the east coast in some areas. (5.5m ish average tide in Northumberland 8.5 ish in Cumbria. Driven by the Gulf stream and of course the moon.
Now, speed is not important as the turbine can be designed to work ona gearbox as the sheer weight of the water is enough to run a very high torque generator. It may only be spinning at 20-50rpm in the water but with so much power available that could generate huge wattage either via a large generator or via a geared smaller generator.
and even as the tide ebbs and floods there is still lateral flow along the coast (ask the folks in Norfolk who's houses are falling into the sea).
Here are the figures for the North West of Scotland and another section of tidal energy. Again it misses the point that if you spread the turbines, you spread the generating times...