The Dutch managed to keep the sea out, we need their expertise on this again. They fixed the Fens 400 years ago, pretty sure they can do London now.
Dutch and English (and US) flood defence engineers work very closely together in terms of sharing best practice, engineering innovation, peer reviews etc. I was at a seminar at the Thames Barrier last week;l and have previously been to the Netherlands. I've been involved in 2 specialist technical groups who meet twice a year or so (Covid allowing).
Whilst parts of East Anglia, Lincolnshire and S/E Yorkshire were reclaimed (or actually just drained and claimed) from the sea (intertidal marshland) by Dutch engineers 400-500 years ago, the physical and political landscapes are very different now (Charles 2nd ordered some of the original work to improve his hunting grounds).
Also, apart from those eastern areas, England I already mentioned, England and the Netherlands have quite different geographies/geological ground conditions. The main form of tidal defence in the Netherlands is to put a barrier around the coast. In England, our defences are a lot more inland. Our governments think differently too!
The Thames barrier is closed on rising tides above a certain height, to stop the tide reaching central London when the river is already full of rainwater. The barrier is actually a series of system of 6 or 7 barriers - the famous big one with the shiny silver hulls across the Thames upstream of Greenwich and smaller (but still significant!) barriers on the downstream tributaries, to manage the water that is pushed up the tribs when the main barrier is closed. Currently the upstream (central London to the top of the tidal limit at Teddington) and downstream (Thames estuary) have more than enough capacity. In 40 years of operation, I believe the Thames barrier has only come close to overtopping once, but the barrier is being operated more and more frequently; more frequently than ever anticipated.
There are also similar tidal surge barriers elsewhere in England, largely in the east.
Technically yes - there are things we can do. We are developing adaptive strategies and all construction works have to adaptable to climate change. As well as physical barriers, flood walls etc there is a massive amount of work looking at upland land management, nature based solutions, offline flood storage (but how do you influence owners of land that doesn't flood, to use/allow to be used for these purposes)? There are already extensive flood storage areas in many locations.
But we are constrained by policy, politics and associated funding. All our work has to be economically viable, and the economic tests are getting harder and harder to meet. It was hard enough to make schemes cost effective once we had to account for climate change, but with the massive increase in material costs in the last couple of years, it's almost impossible at times. Yes, there are projects that will never be delivered due to cost.
I think the big key to more effective flood risk management works will be rooted in funding. Like with all public spending though, increased investments in one area, reduces public money to spend in another.
I have referred a lot to England because the Environment Agency only operates in England, so this is what I know about!