It makes no difference to the safety of the plan, but the additional cost of getting to LGW to start the back-to-back seems likely to whittle your net saving down to practically zero. So why do it, when there are significant disadvantages?

And your reliance on 261/2004 compensation to pay for the cost of missing your onward MCT-BKK flight doesn't take into account the possibility that it turns out to be a zero compensation delay.