Hi Shaun,
First off, you do not have an easycap. You have the real deal. You have an EzCAP. All other manufacturers try to imitate what you have.

It cannot capture in HD. It has to be composite.
So, you need to go with lower quality on your tv when capturing. Your tv will have composite in, somewhere on it.
If you want to record in HD you need to get an "HD PVR". The cheapest I have seen is £170 so there is a huge difference in price.