Shell’s legal team declined to return to England’s High Court with arguments that the five-year-old case would be better heard in Nigeria, according to the parties in the case, conceding that the Nigerian subsidiary will now be joined to claims made in England against the parent company.

The UK Supreme Court said in a landmark ruling in February that Shell’s parent company could be sued in English courts for the actions of its Nigerian subsidiary. The court, however, left the door open for Shell to argue that it was more appropriate to leave any action against the local unit to Nigerian courts. By including the subsidiary in the UK proceedings, more documents about Shell’s work in Nigeria are likely to be made public.

“This is a significant win” for the affected communities because it means they can finally bring their case to trial, Daniel Leader, a lawyer who represents the claimants, said in a statement. However, he added, “Shell’s oil contamination remains in their drinking water, land and waterways, and still no clean-up has taken place.”

Shell declined to comment. The company said in February that it cleans up any environmental damage regardless of the cause...