Buying or selling sterling, without any economic need is very similar to betting, as pointed out by S Barrett in post 34.
For my money, now is not a good time to buy sterling, it has further to fall. While I have acknowledged the point in post 34, I think that due to the unusual nature of the current circumstances, it may well be possible to predict the future trend of sterling. The unusual thing is that a decision has been made but not yet implemented. Usually factors that effect currency movements change from rumour to reality instantly. Brexit if not inevitable, is certainly more than rumour, however it will not turn to reality for over two years.
The time to buy sterling will be when every possible downside of Brexit has been priced in. I have no idea what level of sterling that will be, but it will occur when the markets are really panicking about Brexit. Probably about 6 to 3 months before it actually happens.