Think it is celery - certainly tastes like it....

Assuming this is celery growing on the plot. Is it last years from the previous incumbent or does it look like it will be good for this year?

There's about 12 plants like this in a bed

It looks like parsnip. Dig one up and see. We've just dug the last today, and look forward to giving them a good roasting this evening!

My money would be on celery, which is a biennial, so shall flower this year. But you might get some stalks of it. The seed can be also used in the kitchen though.

As Aidy says, possible to be celeriac, but all those I've grown tend to have darker leaves. And the flavour would be much stronger and earthy.