I have been looking at the parish register, and I think it is possibly T at the beginning.
It looks remarkably similar to the T at the start at Thomas Betwizel's name above it.
I think you have to assume any transcription on any of the sites could be wrong until you see it for yourself. (We all know many, many, wrong transcriptions!).
I've compared the capitals with others on the pages written by the same man.
'F' is on the next page for 'Frodsham', and that would seem to have the horizontal bar across it.
S is written several times ('Seven hundred'), and is a very plain letter.
P is written lower down the page for 'Peter', and that is again different.
I'm afraid searching, albeit quickly, for 'Tirat' doesn't get very far though. Perhaps it too was actually something quite different!
Added:
Ha! You must have gone back and added the clip from the parish regs BumbleB! Good idea.
As to the somewhat strange spellings amberley, you just about hit the nail on the head. As many people couldn't write even their own names at this point, it came down to how the vicar, or whoever was writing it down, to spell it as they thought they heard it. Regional accents would have been still strong in many areas, which would have made it more difficult.
Just to be clear, these are not marriage 'certificates' as you have said in your post several times. They are entries in the parish registers. There were no marriage certificates until 1837 when Civil Registration came into force. They should not be called 'marriage certificates'.