forgot to say, despite having to pay 250GBP for the day at Dibden - it was by far the best interview experience/assessment day I have had in my almost 2.5 decades of working life.
Don't be scared of having to shell out - in the grand scheme of things it's not much money and totally worth it to see how you act in the various tasks and under pressure. You will learn a lot about yourself which is worth the cost, effort and travel.