Hi welcome to the GMB

Sorry, but I think we are going to fail you on all counts, but trying not to be too critical of your questions would suggest you reconsider your thoughts on this piece.
Do you have some reason for feeling sure this bottle is English - glass travels around the globe a lot, and the presence of the piece in the U.K. doesn't confirm this country as its place of origin.
Based on the appearance only of your glass, age is difficult to assess - pieces originating from the C18 would not have been made mechanically, so if this piece has any signs of machine production then it's almost certainly going to be a century or more later than you were suggesting.
Can't see clearly from your pix, but pieces from the C18 would, usually, has some characteristic indicating a hand made aspect - a pontil scar, or ground/polished depression on the base - finding a maker is out of the question, unless the bottle carries any marks to assist, and on balance of probabilities age of this piece is far more likely to be somewhere later in the C19. What in particular makes you suggest an C18 age?

As to value, the people here do not as a rule commit themselves to values, for rather obvious reasons - imagine if we said it was worth £X and it sold for far less - you might feel strongly that our inaccurate valuation had mislead you. Assuming this is a piece with some apothecary connection then you might find something similar on internet auction sites with which to make price comparisons.
This type of glass not remotely my area, though we do have people here who have knowledge of such wares, and hopefully they may be able to add to the above thoughts - have you made any research enquiries to see if this shape does compare with C18 apothecary glass.
Sorry to appear to be negative, but as you can imagine accuracy when making assertions about provenance or age is essential to help avoid mistakes - especially when selling on.

P.S. The Welcome Museum in London has a vast archive and resource of material with medical and apothecary connections - you might contact them if all else fails.