Now is the time to rush and buy all the pounds you can afford to buy. Maybe if you are sharp about Brexit effects on the £, then you may know if to delay a bit to allow the £ to fall even lower.
Otherwise buy it low now. £ pound is not a currency that will stay down for long ,especially in this drastic period of change. £ will make a recovery and it coincides well with this new period of Naira devaluation that may see naira devalue further as the £ finds its way to a quick recovery.
Pound is probably being hoarded as i type this post. But if you can find £ to buy, buy it now and hold on to it.

A good chance to benefit from currency trading.

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