If I suspect my baby had swallowed blu tack, how do I check? Any symptoms to look out for? Is it life threatening to swallow blu tack?

I would just take the LO to the doctor. I actually Googled the composition of blu tack and it says, "The composition of Blu Tack is a manufacturing secret but is described as a synthetic rubber compound without hazardous properties under normal conditions. It can be swallowed without harm and is noncarcinogenic. It is non-soluble and is denser than water." Although it says it's not harmful, I would take them in for a check up.