Medium/long term exposure is typically ALM at the currency level, using debt. Short-term FX change is considered part of everyday business.
Hence, when a treasurer is taking a position, he/she is adding tactical exposure in anticipation of a coming event.
It is highly likely that Brexit will temporarily disrupt UK/EU trade, as well as produce FX discontinuities in Sterling and Euro.
If this is a significant part of the business, it behooves one to purchase a little insurance.
It also implies that 'temporary' Brexit related capital controls are anticipated.
The preference ahead of an anticipated devaluation is to max out the credit lines on the devaluing side, and temporarily transfer the capital to the 'hard' side. Post devaluation, the capital is returned (net of the FX gain), to repay the debt. However, one needs to do it 'early', ahead of any kind of 'temporary' capital control.
These will all be bonusable positions,
and treasurers are not dumb

SD