Hi Duygu/Rumpleteazer
I'll try and shed some light. I've been a UK-based musician, working semi-professionally as a saxophonist and running a band in London since leaving college in 1989.
The towns I know well in the UK are Oxford, Bristol and London. There are lots of small places to play in all of these, though they tend not to be particularly lucrative, and making enough money to live on doing this is hard work. I have two friends - both guitarists - who moved to the UK a few years ago, and have managed to keep themselves going. One was from Australia, and one from Argentina. I know both of them found it very hard work at first. They are both extremely good too. There's a reasonably good number of private engagements available - at weddings and other 'functions' (as they tend to be called there). There are lots of entertainment agencies, bands and bandleaders (like me

who book musicians for these events. Most important things are to be versatile, have a good ear, good sightreading of lead sheets, and to be good company!
The licensing laws in the UK (which govern bars and restaurants) have created a tradition of providing duos as live entertainment. A guitar player and singer or horn player can be good for these. The reason for this is that no special 'Live Performance' licence has been required for up to 2 performers. There's a new (very controversial) law going through at the moment which technically changes this - and not for the better unfortunately. I don't know how that's going to affect things. I'm new to these boards - that may have been discussed in depth here before as it's been a hot topic for musicians for a long time.
Teaching is another possible way to earn money, both privately, and in schools. Let them know you're around, or advertise in local newspapers and music shops.
I've spent a while living in France, and travelling in Germany. It seems like the scene there is similar. If anything, musicians are treated a little better. To work regularly - especially if your friend wants to teach - you'll need to speak the local language reasonably well.
I've written enough! If you have other questions fire away, and I'll try and help. Where are you based right now?
Regards
Andy