Plumbing looks expensive because the smallest jobs expose the pricing most brutally. A tap washer costs £2 to £5 and having one fitted in London costs £60 to £95 including VAT. Once you see where that £70 goes, the number stops looking arbitrary.
You are buying an hour, not a part
The unit being sold is an attended hour. Its cost barely moves with the component, which is why a washer and a valve land in similar territory and why a small job feels worse per pound than a large one.
Inside that hour sits the travel between jobs across South London, none of which anyone pays for directly. A van carrying enough stock that the job finishes on the first visit instead of pausing for a merchant run. Parking, in boroughs where leaving a van outside your house for an hour is a paid transaction. Quoting, invoicing and the calls that did not turn into work. Spread that fixed load over eight hours instead of one and the cost per hour falls, which is why a day is cheaper per hour than an hour is.
Qualification and registration are not optional in parts of the trade
Plumbing is not a licensed trade in general, but its highest-risk work is legally restricted, and that restriction shapes the whole labour market.
Under regulation 3 of the Gas Safety (Installation and Use) Regulations 1998, only a Gas Safe registered person may work on gas fittings and appliances. Doing it unregistered is a criminal offence, not a matter of best practice. Registration is a recurring cost carried by the business and paid for out of the hourly rate.
Unvented hot water cylinder work is regulated separately and differently. It falls under requirement G3 of the Building Regulations, which works through building control compliance rather than the criminal registration regime that governs gas, and it needs a suitably qualified person. That is a second set of qualifications to hold and keep current, and it is another cost the rate carries.
The consequence for a homeowner is that the pool of people who can legally do boiler and cylinder work is deliberately small, and general plumbers cannot expand into it at will. That is a price floor created by safety law rather than by the trade.
Emergency availability is a cost even when nothing breaks
Checkatrade puts out-of-hours and emergency work at up to twice the normal hourly rate, plus a call-out charge. That looks like opportunism until you consider what is being sold: someone who answers the phone on a Sunday evening rather than one who does not.
The same logic runs through call-out charges generally. A booked, non-urgent visit is around £60 excluding VAT; a same-day or emergency one is £110 to £180. You are paying for displacement of other work and for a response time, and those are genuinely different products.
London costs more, measurably
Housekeep, which publishes London and non-London figures separately, puts London at around 20% above the rest of the UK, and its tap figures bear that out: £60 to £95 in London for a washer job against £50 to £70 outside, both including VAT. Checkatrade approaches it differently and gets the same direction, putting London labour on fitting a toilet at £50 to £200 more than the North.
Everything underneath the rate is dearer here: parking, vehicle costs, insurance, and the wage a qualified person will accept to live within reach of the work.
What is not evidenced, and what a cheap quote usually means
Two claims deserve caution. Figures of £100 an hour for London plumbers come from sites with no methodology and no dates, and nothing published supports them. Parts markups of 20 to 25% come from a single source without published method, so ask about parts pricing rather than assuming a standard.
At the other end, a quote well below everyone else usually reflects something removed from the list above: no insurance, no registration for the work being done, no van stock, or no intention of coming back if it leaks. On a £70 job that risk is small. On a boiler it is not.
The costs behind the rate are the same costs a cheap quote has usually left out.