Mr MacCleary met with Rail Minister Lord Hendy and senior representatives from Network Rail and Govia Thameslink Railway on Monday to discuss last week's train derailment near Landport.
During the meeting, Mr MacCleary received an update on the incident and the ongoing recovery effort.
On Saturday, James MacCleary visited the site in Lewes, where he met with senior officials from Network Rail, the British Transport Police and contractors working on the response. The teams remain focused on investigating the cause of the derailment and restoring the railway as quickly and safely as possible.
Mr MacCleary, Liberal Democrat MP for Lewes, said: “First and foremost, I would like to thank our emergency services for their swift and professional response to this incident. I am also grateful to the local community, who came together to support those affected, and to the railway staff and contractors who continue to work tirelessly on the recovery effort.
"During today's meeting, I raised concerns that I have previously expressed about the condition of parts of our rail infrastructure and network. While it is important that we do not pre-empt the findings of the investigation, these concerns must be fully considered as the causes of the derailment are examined.
"We are currently awaiting the initial accident investigation report, and I will be reviewing its findings carefully as soon as it is published. My priority is to ensure that passengers can have confidence in the safety and reliability of our railways.
"For too long, the South East has been overlooked when it comes to transport investment. Despite repeated calls for greater support, the region has missed out in recent Budget decisions. I hope this incident serves as a turning point and reinforces the need for sustained investment in our rail infrastructure and climate resilience, so that passengers can have confidence in a safe and reliable railway."