I have made an interesting discovery. I found that strongly brewed chrysanthamum tea (not from a packet but fresh made with the dried flowers) seems to have a strong anti-hypertensive effect (for me anyway). If i brew it really strong it seems to cause my pressure to fall (100/60) and i feel pretty dizzy.
Interestingly I then found it's a chinese medicinal 'cure' for hypertension too. It seems to have a 'cooling' effect on the body and relieves 'heatiness' of the body under chinese medical thinking.