What are you scanning?
Problem will be sizing it up to A1 -- 594 x 841 mm the picture will pixelate badly if its a standard A4 scanner, you can increase the DPI in photoshop
but the file size will be very large
Is it a single colour logo if so best to scan that in and open it with Adobe Illustrator and redraw it, then it will resize to any size you want and still
have smooth edges
Hope this helps