Thank you all, especially B747-437B for the clear advice.

Will it make a difference if I purchase a ticket from Mexico to London for sometime in Jan/Feb (before the 90 day period allowed under the VWP expires)?

I am planning on applying for residency here in Mexico, but for the type of residency I will be applying for I have to had been in the country for 150 days prior to applying.

I guess the burden of proof is going to be on me. I agree that my links to my home country are tenuous at best.