HI Lucan,
Unfortunately, questions of business valuations often seem to create really negative responses on this board, I'm not sure why.
Because of unrealistic expectations of great wealth. Anyone who has been party to attempted company sales at any level soon discovers a multitude of false expectations and this happens at every level from the multinational takeover (TBH, I have never been anywhere near one of those!) to the sale of what in reality is just a job.
Because I am bilingual and used to work in engineering and trade circles, I was often asked to accompany US and UK companies trying to buy German companies, and/or translate the documentation about such sales.
High valuations are driven by scarcity value- ie what can an acquirer gain by buying you that they just can't get any other way, and what is that value worth to them.
Bingo!
I have seen a factory that no sane person would buy in a million years be sold for a serious sum, simply because they had one solitary patent for a submersible frictionless bearing that would give any manufacturer of submersible motors a huge advantage. A bidding war broke out and a US international won the bidding with a substantial seven-figure offer.
Anyone who saw this factory would find the offer absurd unless they understood the importance of that patent for that market. The place was a mess, there were H&S violations everywhere you looked and as far as profits go, they went a long time ago!
But the company had that patent - and if the competition got their dirty hands on that patent and were able to develop it and extend that patent, it would have been a major disaster!
Your description suggests that you have something with genuine scarcity, but it is too hard to tell from your description how that scarcity turns into actual revenue, and whether the future security is sustainable.
Scarcity alone is never enough. There must be real value as well. A small plot of land in Dresden, enough for one solitary house, is not scarce, but it sold for €1m as it was slap-bang in the middle of a proposed city development.
If the business isn't scalable significantly beyond £70k then you either have a lifestyle business for sale OR its a bolt-on that someone else has to be able to seamlessly manage (which means you need to get the businesses internal processes setup and working....)
The two owners of a German trade magazine run from their homes and with a turnover of about DM150,000 p.a. thought that they could sell to a UK publishing house - but they were the only full-time staff - one bloke on sales and one on editorial, plus a few freelance writers.
"We buy it and then we have to find offices and two full-time staff - and one of our English mags get more turnover from the German market than they do - and all for a lousy £60k turnover! It ain't worth the candle!" is what the publisher said when we put the facts before him. (And that was in the 90s when £60k was the average price of a decent house!)
TBH at the level of turnover you currently have you are going to find it very hard to generate a sale in any meaningful timeframe-you should either approach the obvious buyer with a sale proposal OR why not consider licensing it to them?
See the example of the trade magazine - a turnover of £70,000 is not going to get anybody's juices flowing! The 'Sturm und Drang' of integrating a small and local gateway function into a larger corporate machine is unlikely to be able to generate any meaningful additional profit. You employ just one solitary person extra and all hope of profit is gone.
Sadly, today the fixed costs of any business function are so bloody high that it takes stupid sums just to keep the old nostrils above the waterline! Offices, water and wastewater, bin collection, holiday arrangements, pensions, annual accounts, MTD, VAT, parking, council taxes and rates, heating and electricity - it just goes on and on! Setting something up that is local for £70,000 turnover is just a liability and not a business prospect.
One solitary guy running one small and profitable enterprise is a fine thing - but bringing that one activity into a large company with structures and overheads will just serve to destroy that one small enterprise - I've seen it happen!