I am resitting the sightreading element of the teaching diploma for piano in July. I have all the graded exercise books and play duets regularly. Any other advice and help please as I suspect I'm still not up to the required standard.

I haven't got any advice on getting better at sightreading but the examiners do require a very musical performance with flair. Take careful note of any dynamic markings and any words written in the music. The more shape and colour you put in the better. Keep going and aim for the most musical performance you can muster.
Make sure you practice in lots of different time signatures - they love changing from one to another, eg 4/4 5/4, 7/4 etc. Good luck.

Does anyone know whether the sightreading in the teaching diploma and the quick study in the performance diploma are of the same standard? Do they expect more from you in the quick study than in the sightreading test? Any comments from those who may have done both diplomas?

There are a couple of people on this forum who have done both diplomas. I haven't but I am pretty sure I am right in saying the sightreading level is the same whether teachers or performers diplomas.