Unclear what you mean, Robert: how big is the jar, and is £10 the retail price or the price charged by the beekeeper to the retailer?
£10 is likely to be the retail for a 340 or (if behind the times) 454; the beekeeper may get £6-7 or so. General retail discount is 30-40%, but rather than fuss & juggle over different retailer rates, decide what you want for your honey and let the retailer decide what price to set to the customer.
For example, I have a small local management contract that sells the honey to two local shops at £6.50/235. Retail price is their affair, currently around £8.90, a 38% mark-up. In some areas you will have the upper hand if no regular supply is available, so do not under-price (common among beekeepers).
Still, as JBM said, you're a long way from this part of the venture.
You're in for a shock: beekeeping is a fluid, flexible, at times chaotic and certainly messy job and fixed plannng will take you only so far. Plan first to have far more kit than you believe possible, somewhere to store it, how to use it and simple strategies to recognise and manage swarming, without which you will have no surplus to sell.
Have you
read this book several times?