This dataset relates to measurements of thermal sensitivity of propagation delay in Photonics Bandgap Fibres and is to be published in Scientifc Reports in 2015. The Origin file PBGF_thermalStudy_April2014_UoS_10mBGF.opj is an Origin file that contains the raw data and processed data from the experiment carried at the University of Southampton. The Origin file Data_fromNPLecperiment_Fig.6.opj is an Origin file that contains the raw data and processed data from the experiment carried at the National Physical Laboratory. Details about the experiments (including schematics, etc.) are to be published in the corresponding article in Scientific Reports.