good question - certainly taxed me .....
and your question is in the right place - tax or revenue law
actually when I first read it - I thought this was a hobby - you bought coins and kept them like stamps
actually on re reading ( and you are allowed to clarify if you want ) - "I buy and SELL gold coins as a hobby"
and not "I collect gold coins as a hobby ...."
clearly trade and you need to pay tax
[oops I first thought clearly a hobby (collection of coins) and so clearly NOT a trade - but that just goes to show I should read things more carefully]
read this
http://www.telegraph.co.uk/finance/personalfinance/household-bills/11632478/HMRC-targets-Etsy-eBay-and-Gumtree-sellers-but-when-is-your-hobby-taxable.html
I googled "UK when is a hobby income ?"
You need to know your trade- income and sales
three line accounts sufficient
start here
https://www.gov.uk/self-employed-records/overview
sorry
depending on the profits ( NOT sales) you may need to make a voluntary declaration to the tax man ( you were trading and didnt realise there was a tax charge)
and once you are on the yearly tax form carousel
you MUST sign off at the end and not say - "oo lean year this year no tax form required" because you will get an automatic fine for non-submission
sorry again
BC's tear jerking example of the little old lady throwing tea dances where she charged ....trading profit of ten quid a head hur hur hur
is obviously trading by the way ....
depending on your trading profit - (small do it yourself, large get an accountant to do it) I would employ an acct to do the first year
as this isnt a start-up, you have been doing this for a year or two and so there is a previous tax charge which is negotiable.....
because once up and running they are just three line .....
( they is the tax return)