“there can be no grounds for a suggestion of misuse of public money..”

A BBC report notes that the former parliamentary commissioner for standards, Sir Alistair Graham, has called for a review of the Assembly’s ministerial code of conduct. Not just ministerial, I’d suggest, but for individual MLAs. In light of the arrangements by Ian Paisley Jnr, MLA, and Ian Paisley Snr, MP, MLA, to claim as rental costs, public funds which, by Ian Paisley Jnr’s admission, were used to directly pay off the mortgage on the property when he [Ian Paisley Jnr] was “the mover and shaker” in the purchase of that property, here is what the House of Commons ‘Green Book’: Parliamentary Salaries, Allowances and Pensions [pdf file] has to say about the arrangements for Members’ constituency offices

Rules on the arrangements for Members’ constituency offices
5.12.1. Principles

You must ensure that arrangements for your office and surgery premises are above reproach and that there can be no grounds for a suggestion of misuse of public money. [added emphasis]
5.12.2. Propriety
You must avoid any arrangement which may give rise to an accusation that you – or someone close to you – is obtaining an element of profit from public funds; or that public money is being diverted for the benefit of a political organisation. [added emphasis] The allowances must not be used to meet the costs of leasing accommodation from:
 Yourself (But see paragraph 5.12.9. on using an office in your home)
 A close business associate, or any organisation in which you – or a partner or family member – have an interest
 A partner or family member (which includes relatives by blood and by marriage.)

If the accommodation is leased from a political party or a constituency association, you must ask an independent valuer to assess the property in order
to ensure that it is being rented at no more than the market rate. See also paragraph 5.12.5. on agreements for accommodation and services in combination.
You should seek advice from the Registrar of Members’ Interests if the premises are provided rent free or at a rental below market rates.

For Members of Parliament there is also a limit on the Incidental Expenses Provision they can claim.