How do you write

£12,000

I notice some of the maths books we used had £12 000, using a space instead of a comma.

The second but I still carefully count the noughts.

I suspect it depends on the context. Definitely the 1st way for ensuring clarity.

The first way.

The first. Last week DG’s friend’s Mum put £1,000 into her daughter’s school lunch account because she forgot the decimal point.That will keep her going with school lunches till she leaves🤣

I use the second because it's "tidier" unless pence are involved.
As my more expensive items are not sold online it's probably easier.

Informally, I’d put £12K.

A comma within the ££££ and a decimal point before the .00 “pence” - standard practice since decimalisation.

Sorry to be a pedant, but the secondary school maths teachers, I worked with, insisted the decimal point goes in the middle,
£12000·00

A decimal point goes in the centre of a number.

Whereas here in France we have a comma instead of a decimal point!

£12,000.00 or just £12,000

Just to be awkward I use a space and a colon- £12 000:00 though I don't write such big numbers often!

Marydoll

Sorry to be a pedant, but the secondary school maths teachers, I worked with, insisted the decimal point goes in the middle,
£12000·00

A decimal point goes in the centre of a number.

Surely that depends on the context of the number.
If ££ and pence (even 00) are involved, the decimal point goes before the pence- as established at decimalisation back in 1971
From a guide by the University of Edinburgh
Money
Use the £ symbol, or p as an abbreviation of pence. Write out other currencies in full where possible.
Use the pound symbol before the number, with pounds and pence separated by a full stop
For amounts under £1, use p as an abbreviation for pence
Examples
The cost of replacing a card is £5.00
If you return your library book late, you will be charged 75p per day per book.

So I learn it’s a full stop not a decimal point- Marydoll is of course right - but we needed to define our terms!

most typewriters etc would not have had a decimal point, floating in the middle of the line, so a full stop was the nearest equivalent.
but that not the point ! the OP was querying.
for high value items and to avoid any possible confusion, how about writing it in words also.
although, even there, americans say twelve hundred, where we tend to say one thousand two hundred.
but i can remember at school in middx long long ago that we also said twelve hundred . . .

just realised, OP's goods are much more expensive !
what do you deal in, diamonds ?!
anyway, so twelve thousand three hundred.
do americans say a hundred and twenty three hundreds ??
surely not.
sounds a bit confusing, with the word hundred twice.
i rarely have ever had to read or speak v large numbers.

Not 12k, that would be nice! But in the thousands - just some people can’t believe the price.

£12,300.00

copied and pasted from OP.
does not that mean twelve thousand, and three hundred pounds and zero pence ??
that's how i read it.
am i wrong.

wellbeck That's how I read it.

I read it as "twelve thousand three hundred pounds (and no pence)".

Surely £12,300.00 is the correct British way of writing it. But other countries (and therefore currencies) do use a " . " instead of the comma, I believe.

Thee first, ….with a comma

Tizliz

Not 12k, that would be nice! But in the thousands - just some people can’t believe the price.

so it is twelve thousand +
isn't it ?
now i'm utterly confused.
why do you say not 12K, OP ?

this is a random number, not what we charge!