Our solicitor also received signed contracts back from the purchasers of our house without a deposit and we were very uneasey for 2 weeks until we received the deposit. What use are signed contracts without a deposit? Yeah, you can sue, but what would that cost you, financially and emotionally? Your solicitor should have demanded the deposit immediately and failed to act in your best interests by not doing so, same as ours. I would be extremely dubious about the subject to mortgage clause, sounds like a crowd of messers. Make an ultimatum, deposit or all bets are off.