Thanks for the advice John.
I'm beginning to realise why it is that a lot of N gauge layouts I've seen tend to be large 'tail chasers' with little emphasis on shunting.
I'm sure that it must be something to do with the point blade. One bogie of a locomotive will pass through correctly, but not the other one. And the two 0-6-0's that I have will often fall over at the same turnout as well.
I'll get the pliers out!