the british military slashed budgets considerably after 2008. we've maintained special forces and we decomissioned our last carrier before its replacement was ready. we're back up to 2 carriers now but dont have enough planes to put on them.
we have virtually no stockpiles of artillery and our land forces are small.
Russia have demonstrated the ability to carry out chemical weapons attacks on mainland UK soil.
if a full on exchange we would be out of air defence ammunition very quickly.