Q. I want to buy a new business but the only way I can do that is to increase the mortgage on my house. Will the interest I pay on the extra mortgage be tax allowable for the business?

A. In principle yes, but there are restrictions to prevent improper use of this tax relief. Further restrictions are also proposed from 6 April 2013 (see above). Interest paid on loans used to buy into a partnership or to buy shares in a closely controlled company, or lend to such a company are generally tax allowable. However, it would be best to have a separate loan for this business investment, as when you repay any part of the mortgage the business part will be deemed to be reduced first. You will also have to hold at least 5% of the ordinary shares of the company and work for it for the greater part of your time.

Q. My company is doing well and I'd like a new car, possibly a BMW series 5. Should the company lease or buy this car, or does it make more sense for me to take a dividend from the company and to buy the car personally?

A. As the car is available to you for personal journeys you will be taxed on the 'benefit' of driving that car giving rise each year to a tax bill for yourself and a NI bill for your company at 13.8%.

The company will get a deduction against profits for the cost of leasing the car, but that deduction is limited if the car has CO2 emissions over 160g/km (reducing to 135g/km from April 2013). Likewise the capital allowances are restricted for cars with CO2 emissions over 160g/km. The company can pay for the car's insurance, servicing and repairs, with no further cost to you, the driver. However, if fuel is provided there is an additional benefit in kind to be taxed on you.

In reality the calculations need to take into account other factors such as the cost of insurance and whether you need to borrow money to buy the car. We need to talk about this in greater detail to provide you with the correct advice.

Q. Our company is owned jointly by myself and my wife, and we are both directors of the company. I do most of the work and draw a lot of funds out of the business, so my director's account with the company is often overdrawn. My wife has another paid position, so doesn't draw so much from the company. Her director's account with the company is always in credit. Can our two director's accounts be combined and set-off against each other for tax reporting requirements?

A. Married individuals are taxed as separate persons in the UK, and their income and liabilities cannot be amalgamated to present a better picture for tax purposes. The Taxman is dead against the overdrawn balance on one person's account being set against the credit balance on another person's account, even if those two people are married.

Q. The company provides the sales reps with pay-as-you-go mobile phones, who purchase top-ups when they need them, claiming the cost back on expenses. Does the cost of the top-ups need to be included on the forms P11D for those employees? Does it make a difference if the employee bought the pay-as-you-go phone?

A. Where the mobile phone is owned by the company and the contract is between the company and the telecoms provider, any top-ups purchased for that phone are tax free, as the provision of the phone is tax free. The cost of the vouchers does not have to be reported on the form P11D for each employee. Note this tax free treatment only applies to one phone per employee.

If the phone was bought by, and thus owned by the employee, the top-up vouchers are taxable and need to be reported on the form P11D. The employee could claim a deduction on their tax return for the cost of business calls made with the top-up payments, but this would involve analysing all the calls made into business and non-business calls.

Q. Until 31 May 2011 I was employed as loss adjuster for company A, and I drove 4,400 business miles in my own car for that company in 2011/12. I then joined rival company B, and drove a further 8,080 miles on business, also in my own car, by 5 April 2012. Both companies paid me 40p per mile for those business journeys. Can I claim anything extra on my tax return?

A. Yes. The approved tax free mileage rate for 2011/12 was 45p per mile, for the first 10,000 business miles. However, this mileage threshold applies per employment. As you held two jobs with completely separate employers in the year, and drove less than 10,000 miles in each job, all your business mileage can be claimed at 45p per mile. You can claim £624 (5p x 12480 miles) on your tax return for 2011/12.

Q. I'm worried about the Granny tax. Is this going to affect me? I'm aged 64 with an annual income of around £16,000.

A. The so-called Granny tax is actually a change in entitlement to allowances from 6 April 2013. You are currently entitled to a personal allowance (tax free amount) to set against your income, of £8,105. From 6 April 2013 you will be entitled to a personal allowance of £9,205.

As you will reach age 65 in 2013/14 you may have expected to receive the higher age allowance of £10,500 which is available to people currently aged 65 or over. However, because the rules are changing on 6 April 2013, only those born before 6 April 1948 will be entitled to the age allowance of £10,500, everyone else will get the normal personal allowance. This is not as unfair as it seems as the age allowance will be frozen, probably for ever more at £10,500, but the personal allowance will increase each year, and is likely to reach £10,000 in 2014/15.

Q. I don't have all the figures needed to complete the tax credits renewal form and I'm worried I'll lose my tax credits as the deadline is 31 July. The main problem is, my income is as a musician and I don't know what my total income is until I receive the royalty statements.

A. Don't panic. You are required to return the tax credits renewals form by 31 July, or renew by phone, but you can submit estimated figures for 2011/12. When your self-employed accounts are ready you can submit the final figures and your tax credits award will be adjusted as necessary. As long as you submit final figures by 31 January 2013 you should not lose your tax credits.