Shares of Leeds-based Dart Group, owner of Jet2.com and Jet2holidays, fell more than 15% on Thursday after it warned shareholders to expect increased losses in the second half of the year due to “significant cost pressures such as fuel … plus the necessary continued investment in our products and operations including that required to retain and attract colleagues …”

That’s despite results for the half year ended September 30 that showed revenue up 36% to £2.2 billion and pre-tax profit up 56% to £337.4 million.

“Looking ahead, significant cost pressures such as fuel and other operating charges, plus the necessary continued investment in our products and operations including that required to retain and attract colleagues, are emerging headwinds,” said Dart Group.

“This, coupled with the overall uncertain UK economic outlook particularly related to Brexit and how it may impact on consumer spending, means we remain unclear how demand will develop in the medium term.”

Dart Group’s distribution and logistics business Fowler Welch grew revenue 7% to £88.9 million.

Executive chairman Philip Meeson said: “With winter 2018-19 leisure travel bookings in line with expectations and notwithstanding the important post-Christmas booking period that is still to come, the board expects current market expectations for the year ending 31 March 2019 to be met.

“Looking ahead, significant cost pressures such as fuel and other operating charges, plus the necessary continued investment in our products and operations including that required to retain and attract colleagues, are emerging headwinds.

“This, coupled with the overall uncertain UK economic outlook particularly related to Brexit and how it may impact on consumer spending, means we remain unclear how demand will develop in the medium term.

“However, our strategy for the long term remains consistent — to grow both our flight-only and package holiday products.

“On the assumption that the UK Government secures a pragmatic and balanced Brexit agreement with the EU, the outlook remains bright and we continue to have confidence in the resilience of both our leisure travel and distribution & logistics businesses.”