How often do you have to do this? Its not the first time I see you posting that you need to buy pounds.
You should consider hedging your positions if you have to buy pounds often thereby effectively locking-in the price at 21.66. There' s many ways to kill this cat.
CFDs, futures, forex.
Of the above futures is probably the easiest to use (if you have a share trading account, I'm almost certain they also trade currency futures).
With the above method you'd pay R1 995 for 1 000 pounds today, so you'll need 5 times that, or R9975 initial margin (or deposit, you get this back when the future expires).
Should the pound's price fall, you will lose money on the future, but you will gain money when you do the actual trade to buy the 5000 pounds. The reverse is also true in that if the pound's value increases than the future will be worth more. This delta then effectively erases the amount that you would have had to pay in when you buy the pounds.