I expect the petrol allowance changed. This is what you pay your accountant for. If you don t trust him/her or think you know better then change!
I don t see why you should have to go and find out the answer for yourself - you PAY an Accountant to do the job for you and therefore you are entitled to a reasonable explanation from them. Ring her up again and tell her that you want the situation explaining properly. Find yourself a new Accountant for the next tax year - an approachable Accountant is vital for a small business.
Visit the Inland Revenue site and find out if they re doing any free seminars in your area for people in business. You can go along to them and there s time afterwards to ask individual questions on all sorts of tax issues.It might also be worth speaking to your local CAB. They have quite a lot of information on these sorts of things.Another option is to contact your local Business Link and find out if they have any advisors who are experienced in tax for the self-employed. If they don t, they ll probably know someone who ll give you a free half hour session to go through your questions.I know there s a point where once your mileage goes over it, the allowances reduce but I couldn t tell you where that is.Good luck sorting it out!