Thanks for your question and asking for me.
Your accountant should provide you with an income and expenditure sheet detailing the amounts AND also a copy of the tax/Class 4 Calculation and a copy of the submitted tax return for 2013.
With the car there are two ways of calculating the allowable deduction but whatever method you have to remain with it until you change the car (which you did in the relevant tax year but I shall use the mileage method
So I work things as follows
Travel 25,000 miles first 10,000 miles at 45p = £4500
Millage in excess of 10,000 are 15,000 miles at 25p = £3750
With the mileage method you not claim for the car sale and purchase, but can do if you claimed travel under the actual method (so would have added all the running costs together, and then established the business and total mileage, to establish the business use percentage AND allowed the purchase costs of the new vehicle and added back in what you sold the old vehicle for) so I would need more information to take this forward.
Mobile phone (assuming all business) £30 x 12 = £360
Lunches are not allowable as we all have to eat to live.(unless you had overnight accommodation for any job, then evening meal the night before and breakfast the next morning are permitted as well as the overnight hotel/B&B charge)
Home as an office (if this not exclusively used as an office) £3 a week x 52 = £156
If used only as an office then would need the heating and lighting bills and the amount of habitable rooms (excluding bathroom and kitchen)
Then the paper and ink costs and the printer are allowable and I shall estimate a figure of £500
Accountancy costs £1000 estimated
So Income £64000
Total expenses (based on above) £11,101
Net Income £52,899
£52,899 less £8105 = £44,794
First £34370 x 20% = £6874
Remaining £10424 x 40% = £4146.60
Total tax due £11,020.60
Class 4 National Insurance
Net Income £52899 less £7605 = £45,294
First 34870 x 9% = £3138.30
Remaining £10424 x 1% = £104.24
Total National Insurance due £3242.54
Total tax and Class 4 National Insurance bill for 2012/2013 = £14263,14
If your total bill is for £13800 this would suggest that your accountant has possibly allowed the actual method for travel expenses along with the car purchase and that you did supply the heating and lighting bills (if you have a room set aside just for business)
But this seems about right!
But chase up for the full breakdown of how figures were calculated - so you can be sure yourself, all has been claimed right AND make sure lunches are NOT claimed.