That tube is very easy to knock loose when replacing the fuel pump. Remove the fitting and check the tube fitting in the hold down fitting.
To be sure, you can always hook up a cheap aftermarket gauge to verify you do in fact have
oil pressure. You probably do.
Once you are through, you will probably want to replace that nylon tube with a braided metal tube that will never break or leak. There is a parts store that sells these lines custom made for our cars. Wwwbatinc.net. They will custom make you a braided line with the proper fittings to attach to a British gauge and an American engine.