PRINCE2 is different from other project management qualifications as it provides only a structured framework, which can be tailored and scaled in order to run a project - it does not deal with the softer skills involved in being a project manager, which are covered by other qualifications.
PRINCE2 is compatible with all other project management qualifications as it provides the technical structure of the framework for the project, which will complement the softer skills learnt on other qualifications.
The most popular project management qualification worldwide is the PMI PMP. PMI (US Project Management Institute (www.pmi.org), APM (UK Association of Project Management - www.apm.org.uk) and IPMA (International Project Management Association - www.ipma.ch) all have detailed bodies of knowledge that explain the wider skills needed for a project manager.
We have never mapped PRINCE2 against the national framework of qualifications and so are not able to answer this directly, but we estimate that it would sit at around Level 3.
There is no direct next step after gaining the PRINCE2 Practitioner Qualification as this is the highest level of PRINCE2 award, however should you wish to continue your education in PPM (Programme & Project Management) then we would suggest that you look into taking the PPM Diploma - details of which can be seen at APMG-UK's site.
On 24/25th October 2009 in Washington the GAPPS Board verified a comparison between PRINCE2:2009 and the GAPPS Standard. A copy of this comparison is available to download here - Mapping of PRINCE2 to GAPPS (MS Excel).