Dulcolax pico perles are apparently good and gentle so no tummy cramps like you get with some other laxatives.
You take between 2-4 and they work within 6-12 hours.
I've ordered some from amazon for just in case.
you can have senna or dulcolax , BUT I find them really harsh and give me terrible cramps ( work though !!!) as BB said dulco pico perles are great and my local tesco sells them , they work quickly and are gentle movicol is also great stuff and gentle too xx
psyllium husks are great for most people to prevent constipation ( although dont seem to work for me ...) but just make sure you clear any 'blockage ' first or it will make it far worse xx