Complex sentence: A fishermen's cottages row was under construction in the 1840s however the main developer died and the project abandoned with the area used instead as a walled kitchen garden until the gasworks was built.
Split into simpler sentences: A fishermen's cottages row was under construction in the 1840s. However, the main developer died, and the project was abandoned, with the area used instead as a walled kitchen garden until the gasworks was built.