To be honest there are very few bikes (if any) that won’t ride along canal towpaths and poorly surfaced roads. I do this on a 3 Speed Dutch town-bike and whistle all the way.
1500 quids puts you in reach of a very wide-range of bikes from heads-down-arse-up budget CX racers to all-week comfortable disc-equipped touring bikes.
For leisure/keep-fit and gnarly back-lane touring I have finally went for the jack-of-all trades Genesis Vagabond as my riding needs and preferences are best served by an ‘all terrain’ bike with a bias towards wider-tyres, overall simplicity, comfort. And (as it turnedout) – a butted steel frame set, a decision informed by past bikes/preference. I wasn’t consciously looking to buy ‘CX’ I just saw the bike outside an LBC on my way to trying an MTB – and thought ‘that looks like it does what I want a bike to do’.
Like yourself I knew what I wanted a bike to do, but a demo-weekend is what persuaded me to go for a Vagabond. Other bikes I was looking at before trying it: Raleigh Mustang, Spesh AWOL, Genesis Longitude, Raleigh Royal.
As planned I tried a short demo on the Longitude and loved it but knowing I spend a lot of time on back roads it had to be shelved as couldn’t really afford one bike letalone N+. Then tried a long demo on the Vagabond and it just felt like the proverbial glove. Lucky!
I would go and test-ride some bikes if at all possible. Ideally try a CX racer and an ‘adventure’ type tourer at least to compare lightweight/aggressive vs comfort/utility. You might like something inbetween. But I definitely recommend trying before buying. I’ve only ever gotten a long demo ride once but so far it’s turned out to be the best bike purchase decision I ever made. Extra bonus – coming in under a grand ideally frees up money for some bike-packing kit that people buying such bikes would normally use.
So, in short I recommend think harder about what you want from a bike then try some out throw ia few wild cards though as it turned out my ‘wild card’ demo was ultimately the right one!