AFAIK, the government of the day, doesn't even have to consult Parliament for a declaration of war.
As far as defence is concerned, sending a strong message through military action,would never happen with Labour in the mix at any level, Corbyn et al would happily have us turn the other cheek as Russians or Chinese, were marching down Pall Mall.
The UK and Europe have happily sat by and let the US bear the burden for keeping us all safe, this has to change. I was reading some American, complaining of all the money they are spending on Ukraine, however, a comparison of money spent as a % of GDP puts America seven****th in the list of donors with Denmark and Estonia at the top, even the UK is higher in the list.
Defence is like pensions, people want more but they won't even accept a penny on the ? in tax to pay for it.