£30 for Bluetooth headphones is pretty much scraping the bottom of the barrel. £30 is not a lot of money for wired headphones. Bluetooth headphones have additional electronics that cost money, meaning the everything must cost less to meet the low price.
All £30 will buy is no name brands on the jungle site. If that's all you can spend, then pick the ones with the best comments; although I am sceptical about many of the glowing reviews, whether they are genuine.
Maybe quality is not overly important as long as they work well enough; I don't know. Maybe a cheap unknown brand pair is worth a punt. If they suck, just return them.
For a known decent pair of Bluetooth headphones, such as AKG Y45BT, they will set you back £80.