A computer-implemented method of controlling a transfer via a blockchain, the method comprising the steps: identifying at least one transaction (Tx) on a blockchain which comprises: an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input which spends an output from a previous transaction that is locked by a redeem script hash; for each identified transaction (Tx), generating an incomplete blockchain transaction, wherein the incomplete blockchain transaction is incomplete in that it is missing a cryptographic signature, the incomplete blockchain transaction comprising: a first output comprising a copy of the redeem script hash; a second output which is modifiable such that only the asset controller is able to specify a recipient for the second output; and a signature type which requires that none of the outputs are signed; wherein the method further comprises the steps of: modifying the incomplete transaction so as to include a cryptographic signature; and completing the incomplete transaction by specifying a recipient for the second output and submitting the completed transaction to the blockchain; sending a signal and/or an electronic notification to a notification address which is provided as metadata within an unlocking script of an input of a transaction (Txi) on a blockchain, wherein the signal or notification provides a prompt, trigger or alert to a recipient relating to the incomplete transaction; and in response to the signal or notification, modifying the incomplete blockchain transaction, wherein modification comprises providing at least one cryptographic signature. identifying at least one transaction (Tx) on a blockchain which comprises: an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input which spends an output from a previous transaction that is locked by a redeem script hash; an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input which spends an output from a previous transaction that is locked by a redeem script hash; for each identified transaction (Tx), generating an incomplete blockchain transaction, wherein the incomplete blockchain transaction is incomplete in that it is missing a cryptographic signature, the incomplete blockchain transaction comprising: a first output comprising a copy of the redeem script hash; a second output which is modifiable such that only the asset controller is able to specify a recipient for the second output; and a signature type which requires that none of the outputs are signed; a first output comprising a copy of the redeem script hash; a second output which is modifiable such that only the asset controller is able to specify a recipient for the second output; and a signature type which requires that none of the outputs are signed; wherein the method further comprises the steps of: modifying the incomplete transaction so as to include a cryptographic signature; and completing the incomplete transaction by specifying a recipient for the second output and submitting the completed transaction to the blockchain; sending a signal and/or an electronic notification to a notification address which is provided as metadata within an unlocking script of an input of a transaction (Txi) on a blockchain, wherein the signal or notification provides a prompt, trigger or alert to a recipient relating to the incomplete transaction; and in response to the signal or notification, modifying the incomplete blockchain transaction, wherein modification comprises providing at least one cryptographic signature. modifying the incomplete transaction so as to include a cryptographic signature; and completing the incomplete transaction by specifying a recipient for the second output and submitting the completed transaction to the blockchain; sending a signal and/or an electronic notification to a notification address which is provided as metadata within an unlocking script of an input of a transaction (Txi) on a blockchain, wherein the signal or notification provides a prompt, trigger or alert to a recipient relating to the incomplete transaction; and in response to the signal or notification, modifying the incomplete blockchain transaction, wherein modification comprises providing at least one cryptographic signature.