Labour and the Conservatives say we must continue having submarines armed with nuclear missiles on patrol at all times.
The Liberals are the only ones saying: Let's find a better way of keeping us safe.
Subs with nuclear missiles are the answer to the question: How do we prevent Russia from bombing us?
As the only countries which go to war these days are America and us, having a re-think seems a sensible idea.
Does anyone seriously think today that Russia or China is likely to start bombing us? Terrorist are likely to bomb us; other countries are not.
The two countries which are keen to get nuclear missiles are North Korea and Iran, both of which are more likely than the rest of us, to be attacked by another country.
If we were realistic about this, we should sell our Tridents and our submarines to North Korea and Iran and spend the money on terrorist-prevention instead.
This is no more stupid than spending £20 billion to prevent something which was likely 50 years ago but isn't now.
