I received my new Iphone 6 last week, backed my iphone 5 and then restored my new handset. It has been working fine until today when I deletec all my contacts from my old handset. Contacts have gone from my new handset too, how do I get them back?

If you use iCloud then contacts are stored there, and sync to each of your devices. Changes made on each device are replicated to other devices using the same Apple ID - so in this case, a deletion made on one iPhone will happen on the other one too!

Hopefully you have a back-up somewhere of the iPhone with the contacts on?

The point is not whether you used iTunes or iCloud to restore your new iPhone. It's whether you have Contacts turned on in Settings > ICloud. If you do on both your old iPhone and new iPhone then those devices are connected through iCloud. Deletions on one device are also made on the other.

You may be able to restore your Contacts be using your old device backup to restore your new iPhone again. Make sure that you turn Off ICloud functionality on your old iPhone before you delete anything else from it.

If Contacts are turned on in "Settings > iCloud" on a device and you deleted those Contacts from that device then the Contacts will be deleted from every device that accesses that iCloud account. That's how it works. What you should have done is turn off iCloud for Contacts on that phone first before deleted the contacts.