Carlos Sainz was set to be confirmed as a Williams driver at the Spanish Grand Prix last weekend. But now his future is uncertain once again. Sainz has been the centre of attention in the F1 driver market since the start of the season. This was bound to be the case after Ferrari made him a free agent by signing Lewis Hamilton. Initially, the expectation was that the three-time race-winner would join another front-running team. Toto Wolff says talks over a move to Mercedes reached an advanced stage before the Silver Arrows pulled the plug. They wanted to bide their time, assessing the developme…