Depends which conifer they are - if they're really gigantic, are they Leylandii cypress?

If you cut the sides back beyond the green they won't rejuvenate. However you can take the tops out with no problem as the branches at the sides will then grow upwards and carry on as normal. within a short time you won't be able to tell. A neighbour reduced his by a good six feet.

thank you steragram,did your neighbiur have them cut straight across at the top.i always have mine trimmed and kept in their natural shape as i prefer that so never take too much off them but as it is so expensive to have them all done decided this time to bite the bullet and have the height reduced by quite a lot,havent done it yet.
Sorry spelled neighbour wrong but as youve probably realised from the fact i dont post photographs im no use at this computer lark i get by thats all will have to have some lessons.

Geraldine, we topped our conifers by at least six feet about five years ago and now they need doing again, it seems that by lopping them re-juvinates them and they grow pretty quickly. I would like to take ours out but as you say, the expense!

You don't need to worry about keeping the shape as they will gradually put it right again by themselves over the season. Go for it, give 'em the big chop. You'll be amazed yow much more light you get.