You should always remove the lowest leaves as the fruit sets to allow more light and air around the roots. De-leaving should be a gradual process as suddenly remove too many will cause stress and leaf rolling. I don't see why you can't remove a few of the upper leaves but don't do it all at once.

Are you giving them a high potash feed?

yes it is high potash is this ok

If you want your tomatoes to ripen leave the upper leaves alone.
If not, by all means take them off :)
Leaves can be removed up to the first truss to aid circulation.

Tomato leaves are essential for the complex chemical process that leads to ripening. Sunlight is not needed, just warmth, though the two go together.
Feeds will help with the general well being of the plant, size and flavour of fruit. Too much potash and not enough watering can lead to blossom end rot by preventing calcium uptake, so watering is the most important bit.

thanks

Ethene (ethylene) is the gas that promotes ripening and can be made by several tissues. The best source is ripe fruit so ripening is a bit of a chain reaction.
Commercial growers remove all the leaves from the vines late in the season and pump ethene into the greenhouses.