According to the 'Google Lens' app, which I just downloaded and added to my phone for the purpose of trying to find out what flower this is (BTW my wife uses 'Google Lens' to identify all sorts of garden plants and bugs and loves it!), it could very well be a version of Malva Sylvestris or the Common Mallow. It is a naturally occurring wildflower in the UK and many parts of Northern Europe, has been cultivated as a garden plant in many other parts of the world and has become listed as an 'invasive species' in North America due to it's ability to escape from gardens and take over local habitats!
Lots of info on the Wikipedia page for it here:
https://en.wikipedia.org/wiki/Malva_sylvestris
A Google image search for 'Common Mallow' gives tons of hits that look a lot like the flower in question too and a general Google search indicates that the Mallow family also includes hollyhock and hibiscus so your initial suspicion looks well founded!