Research ahead of Public Service Day reveals how shockingly under-valued our NHS, education, policing and civil service servants are   Nurses have been named as the most under-appreciated public sector professionals by workers in Cardiff.   Almost 5.4m people are employed in the public sector and civil service across the UK but research by public sector membership club Boundless has revealed how rarely they get thanked.   The research, which polled 2004 UK workers in advance of the UN’s Public…