can anyone tell me what this is ?

This looks scarily like horse tail/mares tail.... keep a close eye....

Urgh! Is that growing thro' tarmac??????

thanks i had a look on the internet and it does look like it
it seems to be very strong and yes it is growing through tarmac. which seems weird but thanks for the advice on what it is and it does look horrible !

If it is mares' tail the best you can do is keep a really close watch, don't ever let it develop its leaves (spindle type things that radiate out) and keep chopping it down as low down as you can - if you are vigilant it will weaken, but if it makes any green, it powers up the roots below and invigourates/spreads. Keep your eyes open if you've any open soil nearby and check it doesn't creep along to there - it spreads by long underground roots, and if alowwed to develop, by spores. Nasty stuff - we have it encroaching our garden from both sides (ie both neighbours have it and haven't kept it at bay. We scour the boundaries watchful for any vanguards into our space!

Oooh, I'm glad I've read this question, the things you learn........!!

it looks like horse tail just make sure you don t have red rum under your tarmac!!