Thinking ahead - blackberries

At one end of my plot I've unherited a massed tangle of blackberries(BB's). They are infested with thistles/nettles/etc. It was very difficult last year to pick the fruit as I could only reach in about 2 feet-ish.

What I want to do is to dig the whole area out, get the weed roots out and replant the BB's in more uniform rows which will allow me access to weed/pick.

I'm told that I shouldn't do this until the end of the season when the BB,s are dormant.

My question are:

1, If  I cut the BB's back to enable me to untangle them will they put on growth in the spring to give me fruit next year or will I have to miss a year whilst they re establish themselves?

2, How hard can I cut them back and still stand a chance of fruit next year?

Regards, WG

Thanks for that.

Anyone else got any info that may help?

Regards, WG

I have to say, I'm 100% behind Stompy with this.

My "Loch Ness" is a pleasure to harvest. (Unlike the gooseberries that I've got to tackle soon with full Kevlar body armour).

I bought a thornless variety,also Loch Ness i think 3 years ago and this year i will have masses of lovely juicy big blackberries,it has spread so much now that im going to have to dig my backcurrant bush up as it being smothered by the blackberry,not sure where im going to put it but if its a toss up between the blackcurrant and blackberry i know who will win.......in the words of the great Homer Simpson......mmmmmmmm blackberries

I should have mentioned that our blackberry is the thornless variety, not sure of the name though. It's easier to harvest but still gets out of hand if not heavily checked.