v1.3.8 Shipping Zone Setup

One area of Zen Cart I can't seem to get my head around is the setup of the shipping. What the developer appears to have 'switched on' for me is Next Day | Zone Rates | Standard Shipping.
What I am trying to achieve now is have 3 types of shipping on offer:
UK Mainland 2-3 days adding a cost of £4.50 plus vat
UK Next day delivery £5.19 up to 20 kilos in weight
Islands and Ireland a flat rate of £25

But I am totally confused as the settings in each section under shipping that the developer has installed and enabled Next Day | Zone Rates | Standard Shipping all have different numbers in them. And so at the moment I am getting stupid prices at the checkout telling the customer it will cost £37.50 to ship a £9.78 item.
Can someone help me out as I have lost hours at this:frusty: