Yes, and not rarely. From many UK airports, return flights to cities in Spain, Portugal, Italy, Poland, the Netherlands and Ireland can be found under £50 if you are flexible about dates and travel with only a small bag. One-way fares under £20 are common on the cheapest routes.
What you cannot count on is finding one for a specific date, a Friday evening in August or a half-term week. Those days sell at much higher prices. Think of £50 as a target you can hit with flexibility, not a standard fare.
