To clarify the taxation of rental businesses (and indeed most other businesses). The traditional method of accounting (the accruals basis) is to declare all income DUE in the accounting period, and to claim expenses INCURRED in the same period. That means if a tenant defaults the expected income is still taxable in that period, and (for example) claims for, say, heat and light, are apportioned to the period in which they are consumed (not when you get the quarterly bill but when you use the gas and electricity). If a tenant defaults the unpaid amount can be deducted from income in the period in which it becomes clear that it is not going to be received - for example, having taken the usual steps to recover it (including court action) and basically having no chance of ever getting it. An alternative is to use the "cash basis" which means if a tenant defaults you don't include that in your calculation of earnings for that period, but nor can you deduct a portion of any unpaid gas/electric bill either even if the power was used during the period.
Since online selling sites began I have heard of scores of people bragging about how much money they have made by effectively running businesses in this way. The first I heard of was a retired couple in a relatively smart town in middle England, the wife having a disability and claiming every state benefit possible (mostly non-taxable), making tens of thousands of pounds a year by buying imported toilet rolls by the lorry load and selling them to small independent shops for resale to the public. They declared nothing to either HMRC or to the benefits people so were basically screwing the country in a big way. You and I (who pay our taxes and don't claim benefits to which we are not entitled) have been paying for these people for years. Believe me, it amounts to a lot of millions that could be channelled into making our NHS what it should be, what it used to be, without the Tories claiming the country can't afford it or the Labour lot (hopefully I suppose winning this years General Election) putting up OUR taxes so they can appear to be the good guys.
I have spent a lifetime both in my profession as an Accountant and as a volunteer in local charities hearing of such travesties (and believe me some folks are PROUD of themselves for screwing the system) - and now I am in dire need of the NHS I am beginning to wish I had reported them all at the time.
But to all of you who are worried about selling your old clothes, a few bits of furniture, an unwanted exercise bike (mine is going on ebay this week!) or similar, you have nothing to fear. You won't be making a profit, you won't be doing similar 30 times a year, and if you are unfortunate enough to be questioned on it by HMRC (and a few will be, by mistake), just explain your transactions and it will be fine.
And if you do find (and sell) a Constable in the attic, you can make a Capital Gain of £6,000 a year without paying tax (and if you can show it was acquired by both you and your spouse that is doubled). I had a friend who, many years ago, recently deserted by her husband and left with two young kids and short of dosh, bought a ring from a charity shop for £5 and sold it for £15,000. It is so long ago that I can't remember what claim I helped her make that meant she paid no tax on the gain. I have some sympathy for the desperately hard-up making a bit of money, so my scruples aren't perfect!!
I think this reform is long overdue.