Well those dimensions will give you an image 48.95 X 33.41 cm at 300 dpi or slightly over A3. You could enlarge it, either in photoshop or some other software and easily acheive A2 - so long as the original is of sufficient quality.
I know most people say print at 300 dpi but you can get away with 170 dpi quiet well and sometimes even lower. Its a fact 99.99% of people can not discern the difference between 300 dpi and 170 dpi.
300dpi is just a figure that is used amongst the printing trade for their purposes as thats what their equipment works at. I have been to numerous lectures by profesional image retouchers and printers who all say the same and agree that the human eye can not actually spot the difference once reolution goes above 170 dpi, all you are doing is using extra ink.
As for which companies to use I have heard good reports about photobox and also Pro-am imaging in Bradford, who do large prints at some of the cheapest prices around, eg A3 prints for £1.