Fernando Alonso: "It's obviously not ideal to start the weekend with a brand-new power unit, only do three laps with it, and then have to change it, especially as it means we'll be taking penalties.

"It's not ideal, as I say, but you always prefer these things to happen in practice sessions rather than in races – and it's worse still if you're running in a points-scoring position when such mishaps occur. So let's look on the bright side: as ever, we'll learn from our mistakes and we'll make sure we minimise the incidence of repeat occurrences in the future.

"We'll be starting Sunday's race from the back of the grid, but we'll be trying our best to recover positions from there. I expect Lewis [Hamilton], who'll be starting next to me, will be quicker than me, so I'll try to hang on to his tail, put a rope around his car and get him to pull me through the field!

"I still don't have a feeling for the performance of the revised PU, as today we ran it only in conservative modes, so tomorrow we'll see how much we can push. I'm sure it'll be a step forward."

Jenson Button: "In the end we made a lot of progress today: after making set-up changes following a challenging first practice session this morning, we had a much improved second practice session in the afternoon.

"As a result, we've now achieved a handling balance that works for us, but there's still room for improvement. Our long run was reasonable; we seem relatively competitive, certainly compared to the cars against which we usually race. And we were quicker than Kimi [Raikkonen] on the longer runs, which was good to see.

"Getting through to Q3 is always our aim on Saturdays, but what happens on Sundays is more important still. Put it this way, we didn't get through to Q3 at Hockenheim yet I still finished eighth. And, here at Spa, it's easier to overtake than on most circuits, so I'm feeling reasonably optimistic about the race.

"It's unusually hot here this weekend, but that'll mix things up for the race, which could be good for us too."

Eric Boullier, McLaren-Honda Racing Director: "Today was a tricky day for us, compromised by a number of factors, but we reacted well to those challenges and by the end of FP2 we'd made good progress with regard to finding a decent handling balance.

"As a result our corner speeds were competitive – competitive with anyone's in fact – but we knew in advance that the long and fast Spa-Francorchamps circuit wouldn't suit well the specific characteristics of our car's performance envelope.

"Having said that, the work that both Honda and Esso have done recently, in terms of improving combustion efficiency and turbo/compressor harvesting/deployment, has had a small but discernible positive effect, for which congratulations are due.

"However, we still have a lot of work to do before qualifying tomorrow, and of course whatever Fernando is able to achieve will necessarily be stymied in terms of grid position by his very significant PU-related penalties.

Yusuke Hasegawa, Honda R&D Co Ltd Head of F1 Project & Executive Chief Engineer: "For the Belgian Grand Prix weekend, we've introduced a new ICE with increased combustion efficiency and a new turbo/compressor combination, to increase power unit performance including efficiency for the latter half of the season.

"Unfortunately, during FP1 we found a water leak in Fernando's MGU-H and had to cut short his running time. Based on the situation, we assessed that the MGU-H issue was not a consequence of the update and therefore elected to replace it with the same updated spec for FP2. As a result, we'll incur grid penalties for the race on Sunday. Thankfully the team did a great job in preparing a new power unit to run in FP2, and we were able to get straight back out on track at the start of the session.

"Today's sessions were focused on running the cars with low downforce and checking grip levels, and, despite the power hungry nature of the circuit, we were able to finish in our now usual midfield positions. The initial feedback on the power unit updates has been positive, so we'll look to our engineers to fine-tune for tomorrow's qualifying and Sunday's race."

Check out our Friday gallery from Spa, here.