Vueling is having yet another flash sale on 8th and 9th of August, for flights from 18/10/2017 till 20/03/2018, from €19.99 one way.
Seems like Vueling is holding flash sales every other week! This time it's selling tickets within Europe and Spain, with prices from €19.99 per one way flight.

It's a nice opportunity to grab a bargain, especially if you are located at one of Vueling's hubs: Barcelona (24 destinations on sale) or Rome (17 destinations on sale). There are some flights from London (LGW and LTN), Paris, Zurich and other European cities.

Availability depends on origin and destination, but on Barcelona-London route it seems to be very good from October till February.

Sale tickets are booked into Basic tariff, which includes only hand luggage, no seat selection (it will be assigned to you automatically) and no Avios (but you can still earn Vueling Punto points).
Remember that you need to book by the end of the day tomorrow, 9th of August.
All destinations on sale and sale rules can be found here: http://www.vueling.com/en/promo-winter?utm_source=newsletter&utm_medium=email&CRM=PES_EN_201708_Lastminute_20170808&spMailingID=30073955&spUserID=ODM1MTU2NTU1MDIS1&spJobID=1100777215&spReportId=MTEwMDc3NzIxNQS2