A downhole tubular flow stop valve, the flow stop valve comprising: a housing; first and second receiving portions (126, 128) attached to first and second ends of the housing respectively by attachments arranged between the housing and the first and second receiving portions (126, 128); the attachments being arranged such that a flow is permitted between the housing and the first receiving portion and the housing and the second receiving portion; a spindle slidably received in the first and second receiving portions (126, 128), the spindle and housing together forming a valve to selectively prevent flow through the flow stop valve; and a biasing element, wherein the biasing element acts on the spindle such that the biasing element biases the spindle towards the closed position, wherein the flow stop valve is configured such that a pressure difference acts on the spindle such that the flow stop valve is in a closed position when the pressure difference is below a threshold value, thereby preventing flow through a downhole tubular; and the flow stop valve is in an open position when the pressure difference is above the threshold value, thereby permitting flow through the downhole tubular, wherein the pressure difference comprises a difference between a fluid pressure at the first end of the housing and a fluid pressure at the second end of the housing, wherein a first end of the spindle and the first receiving portion define a first chamber and a second end of the spindle and the second receiving portion define a second chamber, the first and second chambers (134, 138) not being in flow communication with first and second ends of the housing respectively when the flow stop valve is in the closed position; and wherein there is provided a first passage through the spindle from the first end of housing to the second chamber and a second passage through the spindle from the second end of the housing to the first chamber, such that the first chamber is in flow communication with the second end of the housing and the second chamber is in flow communication with the first end of the housing. a housing; first and second receiving portions (126, 128) attached to first and second ends of the housing respectively by attachments arranged between the housing and the first and second receiving portions (126, 128); the attachments being arranged such that a flow is permitted between the housing and the first receiving portion and the housing and the second receiving portion; a spindle slidably received in the first and second receiving portions (126, 128), the spindle and housing together forming a valve to selectively prevent flow through the flow stop valve; and a biasing element, wherein the biasing element acts on the spindle such that the biasing element biases the spindle towards the closed position, wherein the flow stop valve is configured such that a pressure difference acts on the spindle such that the flow stop valve is in a closed position when the pressure difference is below a threshold value, thereby preventing flow through a downhole tubular; and the flow stop valve is in an open position when the pressure difference is above the threshold value, thereby permitting flow through the downhole tubular, wherein the pressure difference comprises a difference between a fluid pressure at the first end of the housing and a fluid pressure at the second end of the housing, wherein a first end of the spindle and the first receiving portion define a first chamber and a second end of the spindle and the second receiving portion define a second chamber, the first and second chambers (134, 138) not being in flow communication with first and second ends of the housing respectively when the flow stop valve is in the closed position; and wherein there is provided a first passage through the spindle from the first end of housing to the second chamber and a second passage through the spindle from the second end of the housing to the first chamber, such that the first chamber is in flow communication with the second end of the housing and the second chamber is in flow communication with the first end of the housing.