It doesn't matter if you're in Poland, the UK, the US, Brazil, Portugal, Spain, Germany, or anywhere else. As long as you use a high-quality VPN, you can play on bet365 from anywhere in the world.
Yes, Bet365 is safe to use. The sportsbook provides various levels of firewall and other protections and the sportsbook itself is regulated by each of the state gaming regulations Bet365 is legal in.