Is this a herb?

Could be a Monarda Didyma aka Bergamot or Bee Balm.

Maybe Lemon Verbena?

Thanks veggie for trying to name that plant but hey Thelms Sanders gets top prize. I'm pretty impressed with her correct identification especially because there were only leaves to identify. Crackerjack pencil goes to Thelma. I googled Monarda Didyma and read it has square stems, red veins in the leaves, a serrated edge to each leaf and a little hairy underneath the leaves. Then went outside and and was able to tick off each characteristic. What a fabulous plant. Fantastic flowers, is a perennial, is aromatic and great spread in a large bed. Can't wait til it flowers. Thanks again Thelma -take a bow.

But, you didnt tell us all that when you asked us to identify it Cheops.

If only you'd told us about the square stems, cheops - that's a giveaway

It's a very bushy plant and you can't see the stems unless you forage. I wouldn't have thought any plant stems in the world were square in cross section. And I never thought to check underside of leaf - nor look closely at the reddish veins but no matter , one can be vague with Thelma around.
I was puzzled as I didn't remember that plant. Don't think it flowered last year which helped me to forget it. It was a new large flower bed which I filled with bought perennials and though I say so myself last summer that bed looked rather grand with a wonderful palette of colours. Now the sad part of the story. In a village close to me there was a centre run by volunteers - a charity which helped young people out of drug taking. There was a cafe, a book shop, a second hand furniture shop but the best part was two huge polytunnels with rows and rows of benches creaking under the weight of potted plants which the volunteers and the young offenders had grown from seed. As good as any nursery but no wages to pay so the plants were as cheap as chips used to be. The plants were established and bursting into bud. I must of got this mystery plant there amongst others from carnations to variegated lavender to red hot pokers and so on. The sad bit is just after Christmas this charity had its funding taken away and this and it's other branches closed their doors. I miss them.

Sad story indeed, cheops. Hope the people that it helped continue to recover.
...........and next time, give us more clues

PS Members of the mint family have square stems http://theseedsite.co.uk/lamiaceae.html

Yeah it is sad. It was nice to get great bargains but just as nice to know you were helping the charity. Sometimes as I browsed through the polytunnels I saw the young 'offenders' watering, planting and so on and I realised these people were helping themselves to be helped not just taking off others all of the time.
Anyway as it appears you don't enjoy a good game of Cluedo Veggie I'll offer more clues next time. X