Thanks xxstyxx so I did some tests and turning off Seamless Mode stops the blur or padding around each tile. I also found this in the help section:
Use a rendering mode that prevents seams appearing between tiles, but also disables some tilemap optimisations which could reduce performance. Turning Seamless mode off can improve performance, but may show seams if the following project properties are not as follows: Letterbox integer scale fullscreen mode, Point sampling, and Pixel rounding on. NOTE: you cannot use different Seamless mode settings on different instances of the same Tilemap object, even across layouts. For correct display, all tilemap instances of the same object type should use the same Seamless mode.
I have changed my project properties and turned off Seamless Mode and that looks like it has solved the problem.
In Construct 2 you may see seams between the tiles but as mentioned above when you preview this the seams are gone.