I do it regularly and often in F (although I do stop in Singapore a lot). Its fine.

If its your first time in F, you will enjoy every moment of it. The bit I used to enjoy most (and maybe still do a bit), is lining up to board with everyone else knowing that you will be personally escorted to your seat and offered Champagne (which I never take btw). Couldn't get the grin off my face.

The flight to SIN is partly a day time flight so make the most of this one while you are awake. You might sleep a lot on the SIN>LHR (especially if you are on SYD time zone) which of course doesn't give you the full benefit of F (meaning sleeping in F and sleeping in CW is not that much different really).

It can be busy. Which seat do you have?