Complex sentence: But, the Environment Agency projects that expected sea level rise due to climate change will require much increased investment to expand protective measures, an estimated (pounds sterling) 18 million during the next 100 years.
Split into simpler sentences: But, the Environment Agency projects that expected sea level rise due to climate change will mean that current measures will not be sufficient. Much increased investment would be required to expand protective measures, an estimated (pounds sterling) 18 million during the next 100 years.