The driver on the T1-3 carpark shuttle told me that they often get people doing this.
I wondered if people park in T5 long-term when flying out of and returning just to T2-3? It would potentially mean parking at the lower T5 long term rates but being able to take advantage of the closer proximity of the T2-3 Business car park and more frequent shuttle bus.
After all, the T2-3 long term-car park proper is a huge distance away in comparison - right at the south-eastern end of the airport boundary, almost at the A30 / Hatton Cross.