@Mark-Davies-1 This will not cause you problems, all GPS units have a little inaccuracy as do the various maps that are used. Here is a section of your route using the Here map with the compare with tool turned on showing TomTom's track. This is nothing to worry about.
The TomTom's algorithm also thinks that there is a faster route as can be seen here:
There are other reasons like traffic density that may send you on a different route than the one you thought you'd planned. My advice would be to use the compare tool and add a few more route points to force your device to take your designed route.