There are many layers to this story. First the United Kingdom is no slouch when it comes to security and counter-terrorism. The Special Air Service (SAS) and Special Boat Service (SBS) have been used as models for other counter-terrorist groups (such as the US Delta Force). The UK government had to deal with the Provisional Irish Republican Army (PIRA) bombings and assassinations for decades. New Scotland Yard has had to deal with a huge increase in criminal organizations that are as heavily armed as any American gang.
The United States complaints seem to have to deal with not enough security personnel by the UK. In response, the US is sending the FBI and diplomatic security. The response indicates the US government is much more concerned about retaliation either for the past Global War on Terror, the air campaign against Libya, or perhaps anticipated future hostilities with Iran. The choice of the FBI is intriguing. I understand the need for a law enforcement agency but I would have thought the Secret Service and Department of Homeland Security would have been the preferred choice in this circumstance.
The United States is becoming more adept at straining relations with former allies. While I agree the 2012 Olympic Games pose some very grave concerns, embarrassing a long-standing ally does not make sense.