My partner and I have never owned a house in the UK and are first time buyers.  If we buy a new home for £300,000 on a joint application, will stamp duty still be payable?

Stamp duty land tax (SDLT) is still payable. In March 2010, the Chancellor introduced a new relief for first time buyers from SDLT until March 2012 where the purchase price is not more than £250,000. Your question was presumably that since you are buying the property jointly with your partner, maybe the £300,000 price is deemed to be two purchases of £150,000 each, and so you would still qualify for the relief. However if you look on http://www.hmrc.gov.uk/budget2010/march/sdlt-qa-tech-1545.pdf, you can see in Q.10 there that ‘the sum for the whole of the purchase must not exceed £250,000’.