Well, one way to avoid 'declaring profits I've not exactly made' is the write the stock off as you buy it and only show it as contributing to profit if and when it is sold.
You clearly know something about stock valuation in commercial/industry because of your job. Businesses have to do that (stock taking) because 'stock' contributes massively to justifing the value of the organisation and the profit is created when some (hopefully ALL) of that stock is sold for more money than the value put in (through its original purchase and any added-value from processing it - you're a Distributor, so this last bit doesn't really apply to your business).
If you are a sole trader and you are essentially saying to HMRC, 'look I've bought this and sold that, spending xyz in the process. That leaves this amount, all of which I've taken out of the business (an income)'. You could start off like that and it sure would depress your net income - because you'd be building up 'stock' that you'd be recording as having zero value.
Its not the way you can continue to do it for long because you are going to have to start producing a simple profit-loss and balance sheet at some time if the business grows - and in doing that you are going to have a value unsold stock (perhaps at its cost price) so that your business holds a sum of work-in-progress stock. In that profit / loss statement, you'd show (to HMRC) that you have had net 'drawings' - i.e. your income taken out the business - on which you pay personal income tax.