This is a wide ranging discussion depending needs, expectations, and budget as a start.
Being in Europe, I would strongly suggest you look towards Victron charge controllers for solar panels. Right now I am finding Renogy "portable" panels to be priced well compared to things like the GoalZero series.
A $50USD Renogy 21W solar panel charger is good for cellphones and similar things but, be aware that Winter and UK "solar hours" are limited so production will be low so, a powerhog Iphone may not fully charge in one 'solar day'.
A couple 100W portable Renogy panels with a simple Bluetooth enabled Victon MPPT charge controller will put out reasonable power for modest needs.
In the UK, unless you are outside the city and away from other building, trees, hedges, etc., you aren't going to get enough Sun on the solar panels to be effective IMHO.
Not a super "green" approach but, an inverter run off a car and car battery is easily achievable by most people assuming you can afford gas/petrol. Something like the Honda EU1200i generator is an awesome option but, a bit spendy for most people. Those Honda generators work for a really long time and are relatively cheap to run as well so, not as crazy as it first appears.
I have 35Kwh of LiFePo4 batteries and ~4Kw of panels at the moment so, judging the merits of a gasoline powered generator took a while for me. The Honda generator makes power on a cloudy days and overnight if needed. Being able to top off batteries or run electric household appliances is nice as well. In my case in the USA, costs for a 1,000W to 1,200W Honda generator range from $800 to $1200 depending on where, when, and how you shop.