It won't go through the hole.

On April 2nd. Royal Mail introduced a revised pricing structure, supposedly to make sending letters and parcels simpler, with fewer price bands - but, effectively almost doubling the cost of sending many items.
Unfortunately, I was caught in the middle of this price increase, as I had listed three items on eBay during the previous week, with postage priced at the previous rates.
The increase on two of the items was not huge; rising from £3.65 to £4.10, but on the third, the increase almost totally wiped out the selling price of the item.
The problem was, that although the item was very light (just over 100 grams), it was fractionally larger than the permitted size for the lower price band. The method of assessing the size, is whether or not the item will fit through a letter box. The local post office had a piece of plastic with a letter box shaped hole in it to test this.
So, I had to pay £6.75.
What really annoyed me was that the service I used was First Class Recorded, which requires a signature from the recipient, thereby requiring him or her to open the door, enabling the parcel to be passed through a hole somewhat larger than a letter box.

The general feeling is that Royal Mail is being fattened up for privatisation, however, I suspect that customers will just seek more cost effective alternatives.