For Stage 1 or Stage 1+ tuning:
Absolutely. A well-executed Stage 1 or Stage 1+ tune will not impact the general reliability of your vehicle and can offer noticeable performance gains while keeping it practical for daily use.
For Stage 2 and heavily modified vehicles:
The simple answer is NO.
If you rely on your car for work, school runs, or daily commuting, then modifying it heavily is a terrible idea. A highly modified vehicle will break down at some point—it’s not a question of "if," but "when." You will end up stranded at the side of the road, and at some point, the car will likely be off the road for weeks or even months.
If you can afford a heavily modified car, you should also have the funds for a cheap £500 diesel to use as a backup.
Just to clarify: We do not accept any claims or concerns about your only car being off the road due to modifications. If you want a modified car, welcome to the real world.