I have a house orchid with last years spike still attached should i cut this back before growth begins for new flowers?
If it's still green, no, because the spike will produce more flowers.
If, however, the spike is brown and dry, yes.
You do not say what type of Orchid you have. Most common are the Phaelinopsis (I am sure that is not spelt quite correctly) but also know as the Moth Orchid.
I have a large collection and all stems which have finished flowering should be cut right back to their base - inspite of some advice you may receive. However, if any new shoots are coming off the old stem, only cut the old stem to above the new shoot so that it can develop and produce more flowers. If there are no shoots coming off the stem, cut it right back and put the plant in a bright position and water when necessary. All you need to do then is wait between 2 amd 6 months for new stem/s to develop between the leaf joints.