Distribution system operators' roles are evolving from a "fit-and-forget" approach towards an active management of their distribution grid. With this approach flexibility management at the local level can defer or avoid costly reinforcements and have a more efficient use of existing assets. Flexibility tenders are emerging as a mechanism that allow DSOs to procure flexibility for the medium to long term. This works proposed a modular framework to analyze the market rules of local flexibility tenders for the participation of distributed energy resources (DER), with a particular focus on demand response and electric vehicles, and applied it to the case study of UKPN's flexibility 2018/2019 tender and Enedis proposal for flexibility procurement. These tenders have been built to allow the participation of DER, but still there are barriers that may hinder their optimal participation, especially regarding connection procedures and baseline definition.