I am a british national with a house in Claremont, Florida. Due to family estrangements/commitments in the UK, the tenant in Florida has failed to pay rent for the property for almost 2 yrs. We keep talking to the letting agent who placed the tenant and checked the references, about placing a lien and eviction notice on the tenant and his business. Do we need to go through the agent or can we do it ourselves. What is the process??

TWO YEARS?

I don't know you would put a lien on, but you should have filed for eviction long ago. Next, you sue the tenant for your losses. Then, if you obtain a judgment, then you can attempt to seize or lien any assets.

You file for eviction and get them out of the house, include that for all unpaid rent, you then get a judgement for payment of all money, only then may you put a lien on property or bank accounts they may have.

... Do we need to go through the agent or can we do it ourselves. ...

The agent cannot go to court in your behalf (unless the agent is also licensed to practice law in Florida), if that is what you are asking. He/she can, however, connect you with an attorney who can go to court and get the tenant evicted.

Yes, technically it is possible to represent yourself, but only technically. Get yourself an attorney.