Damage to the environment as a consequence of exploration, production, imminent depletion, use of fossil fuels and concerns over climate change (increasing lifecycle greenhouse gas emissions), has increased the need for a more eco-friendly, renewable and sustainable source of energy. The level of biodiesel production has been increasing over the last twenty years, reflecting a rapid rise in demand due to its availability, renewability, lower gas emissions, non-toxicity, and its biodegradability. The impact of CO2 emissions on climate change, worldwide industrialisation, countries not having oilfields and need for a strategic and alternative source of energy have also driven an ever increasing demand. Biodiesel is mainly produced in industry by the transesterification process of triglycerides with low molecular weight alcohols using homogenous acid or base catalysts. However, the biodiesel industry faces some significant challenges; (i) high cost of biodiesel feedstock and (ii) the cost of biodiesel processing, including separation, purification and the neutralisation of by-products. These issues can be resolved with catalysts that are highly tolerant to moisture and free fatty acid (FFA) in feedstock oils. Solid acid catalysts have shown promise as catalysts in the simultaneous esterification and transesterification to overcome these issues. Here, lab-scale biodiesel production from simultaneous esterification and transesterification of used cooking oil (UCO) over different developed novel solid acid catalysts has been investigated. The synthesised catalysts, including TiO2/PrSO3H, Ti(SO4)O and SO_4^(2-)/Fe-Al-TiO2, were characterised via XRD, SEM, TEM, TEM-EDS, EDS-mapping, FT-IR, DRIFT-pyridine, TPD-MS with n-propylamine, TGA/FT-IR, CHNS analysis, DSC, TGA, N2 porosimetry, VSM and XPS. The effect of different process parameters on the fatty acid methyl ester (FAME) yield over different catalysts was also studied, including the effect of reaction temperature, mole ratio of methanol to UCO, time of esterification/transesterification, and amount of catalyst to UCO loading in order to achieve the optimum process conditions to obtain the highest FAME yield. Furthermore, a significant aim was to design a highly active, low cost, stable, easy recoverable, FFA tolerant and highly re-usable solid acid catalyst for biodiesel fuel production. It was found that SO_4^(2-)/Fe-Al-TiO2 performs well under optimum conditions of 2.5 h of reaction time, 3 wt% of synthesised magnetic catalyst to UCO ratio, 10:1 methanol to UCO mole ratio and 90 oC reaction temperature for simulations esterification and transesterification processes. A massive improvement in catalytic stability, easy recovery (using external magnetic field), high tolerance to FFA and water have been achieved via the introduction of alumina and iron oxides to the catalyst support. The synthesised biodiesels from UCO over different solid acid catalyst processes were analysed in accordance to ASTM D6475 and EN14214 standard methods to determine characteristic fuel properties such as kinematic viscosity, density, flash point, FAME content, LAME content, and acid number.