I generally charge in fifteen-minute blocks, at a rate of £30 per hour.  Therefore, a 40 minute job would be three fifteen-minute blocks – £22.50. I do not ask for a call-out fee. Likewise, if I need to visit your house to do an estimate, there is no charge for this.

The bill for a typical job would include a couple of elements besides labour:
Materials: this usually includes anything which becomes part of your property. E.g. cement, timber, screws, copper pipe, door locks, etc.
Consumables: anything which gets used up (or worn out) during a job. E.g. water-treatment chemicals, fence paint, blades, drill bits.
Tools: tools have a finite life, and eventually need replacing. Each invoice includes an amount to reflect wear and tear on tools. This is usually a small sum (£1 – £15 or so, depending on the job) because tools do last quite a while.

On the other hand, I can quite understand that people sometimes prefer the certainty of a fixed price for a job. I’m happy to quote on that basis but I’d need to allow for the fact that unpredictable problems frequently occur (e.g. old plaster falling off walls or corroded screws shearing off). I would therefore add 40-80% (depending on the nature of the work) to cover the time needed to solve potential problems. What often happens in this situation is that the job takes much longer than expected, or else everything goes smoothly and no problems arise. Either way, one of us ends up out-of-pocket, which doesn’t seem fair to me.

Estimates
Many jobs are quite straightforward, such as hanging doors, resealing showers and baths, hanging pictures or fitting new taps. For these sorts of jobs, I don’t really need to visit you and can give you a good idea of cost over the phone or by email / text message. This approach allows me to spend more time getting jobs done for my customers and helps to keep my costs down. For other jobs, I would need to have a quick look in order to get a clear idea of the situation.

Just as an idea, here are some rough prices for various jobs. They are based on average times needed to do each job. However, times can overrun or be shorter than expected.
Hanging one internal door, including fitting a lock and handles £60-70 (including tools but NOT materials).
Resealing a bath / shower approx £50 (materials and tools included).
Hanging two small / medium clocks, pictures or mirrors approx £7-15 (including materials and tools).
Hanging large clock, picture or mirror approx £7-15.